[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fyQ0V3pePSl9UjBvJMTxuswXeEAsZUS5fEamocWVeKco":36,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":305,"$fucxFBm2ZjZfGSdmdRaSNGBI_F0jJme4f0GTvzUhQfL8":370},[4,8,12,16,20,24,28,32],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Authors","authors","\u002Fauthors\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"title":33,"slug":34,"path":35},"Tags","tags","\u002Ftags\u002F",{"type":37,"data":38},"blog",{"slug":39,"title":40,"description":41,"seoTitle":42,"seoDescription":43,"author":44,"createdDate":45,"lastUpdatedDate":46,"draft":47,"category":48,"image":49,"body":50,"faq":51,"commentsClosed":47,"tags":76,"related":78,"comments":301},"oxidase-test-principle-procedure-and-oxidase-positive-organisms","Oxidase Test: Purple in 10 Seconds, Delayed, or a False Negative?","Purple in 10 seconds is positive. Purple at 90 seconds means something else. No color at all from a TCBS or MacConkey plate often means the test failed, not that the organism is negative. Learn to read the oxidase test the way a bench microbiologist does.","Oxidase Test: 10-Second Procedure, Controls, and False Results","Perform the oxidase test within the correct reading window, use appropriate controls, and recognize media, reagent, and timing causes of false results.","Acharya Tankeshwar","2012-12-29","2026-08-05",false,"biochemical-tests",null,"A district hospital laboratory in the Terai receives 40 stool samples in a single morning. Watery stool, no blood, no fever. The clinicians are asking one question: is this cholera?\n\nThe technician plates on TCBS. Overnight, yellow colonies appear, exactly as expected for a sucrose fermenter. She picks a colony straight from the TCBS plate, rubs it onto oxidase reagent paper, and waits.\n\nNothing. No purple. Not at 10 seconds, not at two minutes.\n\n*Vibrio cholerae* is oxidase positive. Every textbook says so. The colony in front of her is oxidase negative. She writes \"not Vibrio\" and moves on.\n\nShe is wrong, and the reason is not the organism. It is the plate. *V. cholerae* ferments the sucrose in TCBS and floods its immediate surroundings with acid. Below roughly pH 5.1, the cytochrome c oxidase reaction simply will not run, no matter how much enzyme the organism has. The colony was positive. The test could not say so.\n\nThe oxidase test is the first branch point in every Gram-negative identification you will ever do. It is also one of the easiest tests in microbiology to break. This article is about the second half of that sentence.\n\nThe oxidase test asks one question of a Gram-negative organism: does your respiratory chain end in a cytochrome c oxidase? A purple color within 10 seconds says yes, and in that moment the organism has left the Enterobacteriaceae. A colorless paper says no, or it says the test was set up in a way that made a positive result impossible. Learning to tell those two situations apart is most of what this test actually requires.\n\nThe enzyme detected is cytochrome c oxidase, also called cytochrome aa3 or complex IV of the electron transport chain. Pseudomonas, Vibrio, Neisseria, Campylobacter, and Helicobacter are positive. Escherichia, Klebsiella, Salmonella, Shigella, Proteus, and every other member of the Enterobacteriaceae are negative.\n\n## Oxidase Test Principle\n\nThe oxidase test is used to identify bacteria that produce cytochrome c oxidase, an enzyme of the bacterial electron transport chain.  When present, the **cytochrome c oxidase** oxidizes the reagent **(tetramethyl-p-phenylenediamine dihydrochloride)** to **indophenols**, a purple or dark blue color end product. When the enzyme is not present, the reagent remains reduced and is colorless.\n\n![ - Mechanism of the Cytochrome Oxidase Reaction](\u002Fblogs\u002FMechanism-of-the-Cytochrome-Oxidase-Reaction.png)Figure: Mechanism of the Cytochrome Oxidase Reaction\n\n![Oxidase test result](\u002Fblogs\u002FOxidase-test-result.gif)Figure: Oxidase test result\n\n### Why Enterobacteriaceae are negative: the branched respiratory chain\n\nA common misreading is that oxidase-negative organisms cannot respire aerobically. *E. coli* respires aerobically perfectly well. It grows on nutrient agar in air. So why is it oxidase negative?\n\nBecause bacterial respiratory chains are branched, and they do not all terminate the same way.\n\nThe test reagent, TMPD, is an artificial electron donor. It does not enter the chain at the beginning. **It donates electrons at the level of cytochrome c.** For the reagent to be oxidized to the purple indophenol, the organism must possess a terminal oxidase that accepts electrons *from cytochrome c*. That is cytochrome c oxidase.\n\nEnterobacteriaceae terminate their chain in **quinol oxidases** instead: cytochrome bo3 under high oxygen, cytochrome bd-I under low oxygen. These accept electrons from the quinone pool, upstream of where TMPD sits. The reagent has nothing to hand its electrons to. It stays reduced. It stays colorless.\n\nSo the oxidase test does not measure \"can you use oxygen.\" It measures \"does your chain pass through cytochrome c on the way to oxygen.\" Every confusing result in this article follows from that one sentence.\n\nAll bacteria that are oxidase-positive are aerobic and can use oxygen as a terminal electron acceptor in respiration. This does NOT mean that they are strict aerobes. Bacteria that are oxidase-negative may be anaerobic, aerobic, or facultative; the oxidase negative result just means that these organisms do not have the cytochrome c oxidase that oxidizes the test reagent. They may respire using other oxidases in electron transport.\n\n### Oxidase test vs catalase test — key differences\n\nStudents frequently confuse these two tests. Both are rapid enzyme detection tests used early in bacterial identification, but they detect completely different enzymes and serve different diagnostic purposes:\n\n| Feature | Oxidase test | Catalase test |\n| --- | --- | --- |\n| Enzyme detected | Cytochrome c oxidase | Catalase |\n| Reaction | Oxidation of test reagent by cytochrome c oxidase | Decomposition of H₂O₂ → H₂O + O₂ |\n| Positive result | Purple\u002Fdark blue color within 10 seconds | Vigorous bubbling within 5–10 seconds |\n| Reagent | TMPD (tetramethyl-p-phenylenediamine) | 3% hydrogen peroxide (H₂O₂) |\n| Primary use | Differentiates oxidase-positive gram-negative rods (Pseudomonas, Neisseria, Vibrio, Campylobacter) from Enterobacteriaceae (oxidase-negative) | Differentiates Staphylococcus (positive) from Streptococcus and Enterococcus (negative) |\n| Applied primarily to | Gram-negative organisms | Gram-positive cocci |\n| Can use nichrome loop? | No — false positive | Yes — acceptable |\n| Can test from MacConkey? | No — false result | Yes — acceptable |\n\nIn a typical gram-negative identification workflow, the oxidase test is performed first, before [TSI](https:\u002F\u002Fmicrobeonline.com\u002Ftriple-sugar-iron-agar-tsi-principle-procedure-and-interpretation\u002F), SIM, urease, and other biochemical tests because a positive oxidase result immediately removes the organism from the Enterobacteriaceae and directs testing toward non-fermenters.\n\n→ [Catalase Test: Principle, Procedure, Results](https:\u002F\u002Fmicrobeonline.com\u002Fcatalase-test-principle-uses-procedure-results\u002F)\n\n## Test requirements for Oxidase test\n\n- Moist filter paper with the substrate (1% tetramethyl-p-phenylenediamine dihydrochloride), or commercially prepared paper disk, wooden applicator stick, or platinum wire.\n- Kovács oxidase reagent (1% tetramethyl-p-phenylenediamine dihydrochloride in water). Store refrigerated in a dark bottle for no longer than 1 week.\n\n![Various types of Oxidase test - Various types of oxidase test procedure](\u002Fblogs\u002Fvarious-types-of-oxidase-test.png)Figure: Various types of oxidase test procedure\n\n## Procedure of Oxidase test\n\nOxidase test can be performed in various ways. These include, but are not limited to, the **filter paper test**, **filter paper spot test**, **direct plate method**, and **test tube method**.\n\n### Filter Paper Test Method\n\n1. Soak a small piece of filter paper in 1% Kovács oxidase reagent and let it dry.\n2. Use a sterile loop to pick a well-isolated colony from a fresh (18- to 24- hour culture) bacterial plate and rub it onto treated filter paper.\n3. Observe for color changes.\n\n> Note: Nickel, steel and other wire loop give false-positive results, so one should use platinum or inert transfer loop. The alternative options are glass rods, wooden sticks, sterile plastic loops, sterile toothpicks and sterile swabs.\n\n![Oxidase test filter paper test method - Oxidase-positivePseudomonas aeruginosa(left) andoxidase-negativeEscherichia coli(right).](\u002Fblogs\u002FOxidase_test_filter-paper_test.png)Figure: Oxidase-positive *Pseudomonas aeruginosa* (left) and oxidase-negative *Escherichia coli* (right).\n\n### Filter Paper Spot Method\n\n1. Use a loop to pick a well-isolated colony from a fresh bacterial plate and rub it onto a small piece of filter paper.\n2. Place 1 or 2 drops of 1% Kovács oxidase reagent on the organism smear.\n3. Observe for color changes.\n\n![Oxidase test on filter paper - Oxidase-positivePseudomonas aeruginosa(left) andoxidase-negativeEscherichia coli(right).](\u002Fblogs\u002Foxidase-test-on-filter-paper.jpg)Figure: Oxidase-positive Pseudomonas aeruginosa (left) and oxidase-negative Escherichia coli (right).\n\n### Direct Plate Method\n\n1. Grow a fresh culture (18 to 24 hours) of bacteria on nutrient agar or [trypticase soy agar](\u002Ftryptic-soy-agar-tsa-composition-preparation-uses\u002F) using the streak plate method so that well-isolated colonies are present.\n2. Place 1 or 2 drops of 1% Kovács oxidase reagent on the organisms.\n3. Do not invert or flood plate.\n4. Observe for color changes.\n\n![ - Oxidase-positive Vibrio choleraeshowing purple colonies, and oxidase-negative Escherichia coliwith lack of color change](\u002Fblogs\u002Fdirect-oxidase-testing-method.jpg)Figure: Oxidase-positive Vibrio cholerae showing purple colonies, and oxidase-negative Escherichia coli with lack of color change\n\n### Test Tube Method\n\n1. Grow a fresh culture (18 to 24 hours) of bacteria in 4.5 ml of nutrient broth (or standard media that does not contain a high concentration of sugar).\n2. Add 0.2 ml of 1% α-naphthol, then add 0.3 ml of 1% p-aminodimethylaniline oxalate (Gaby and Hadley reagents).\n3. Observe for color changes.\n\n![Test tube method of oxidase test - Oxidase positiveNeisseria sicca(left) and oxidase negativeStaphylococcus aureus(right)](\u002Fblogs\u002Ftube_oxidase_test-tube.png)Figure: Oxidase positive Neisseria sicca(left) and oxidase negative Staphylococcus aureus(right)\n\n### Reading the result\n\n**Kovács reagent (filter paper, spot, and direct plate methods)**\n\n- **Purple in 10 seconds**: oxidase positive.\n- **Purple at 60 to 90 seconds**: delayed positive. See below.\n- **No color, or color only after 2 minutes**: oxidase negative.\n\n**Gaby and Hadley reagent (test tube method)**\n\n- **Blue in 15 to 30 seconds**: oxidase positive.\n- **Purple at 2 to 3 minutes**: delayed positive.\n- **No color**: oxidase negative.\n\n**Purple in 10 seconds**\n\nThis is the only unambiguous positive. The reaction is fast because cytochrome c oxidase is abundant and TMPD is a small molecule that reaches it immediately. Speed is diagnostic information, not just a stopwatch detail. A *Pseudomonas aeruginosa* colony goes purple almost as the loop lifts.\n\n**Delayed oxidase reaction**\n\nPurple appearing at 60 to 90 seconds is reported as a delayed positive, but it should also make you suspicious of your own technique. Genuine delayed positives are uncommon and are seen with some *Pasteurella* and *Aeromonas* isolates. Far more often, a delay means the culture is older than 24 hours and metabolically slow, or the inoculum was too light.\n\nColor developing after 2 minutes is **not** a delayed positive. It is autooxidation of the reagent by air, and it happens on a blank paper with no organism on it at all. Run a reagent-only paper alongside your test and you will see this for yourself.\n\n**False negative oxidase test**\n\nThe three causes, in order of how often they occur:\n\n1. **Acidic growth medium.** Sugar fermentation drives local pH below 5.1 and the reaction stops. Lactose on MacConkey, sucrose on TCBS. This is why the *V. cholerae* colony in the opening reads negative. Subculture to nutrient agar or 5% sheep blood agar and repeat.\n2. **Old culture.** Beyond 24 hours, enzyme activity falls. Use an 18 to 24 hour culture.\n3. **Reagent age or exposure.** Kovács reagent oxidizes in light and air. If the bottle or the paper is already purple, throw it out.\n\nA false negative is far more dangerous clinically than a false positive, because it silently reclassifies a non-fermenter as a member of the Enterobacteriaceae and sends the entire downstream workup in the wrong direction.\n\n## Uses of oxidase test\n\n- Oxidase test is most helpful in screening colonies suspected of being a member of the *Enterobacteriaceae* family; all the members of the Enterobacteriaceae family including *E. coli* are oxidase negative.\n- To avoid misidentification, perform an oxidase test on all Gram-negative rods. Oxidase test is especially important in separating *Aeromonas* from Enterobacteriaceae.\n- **Note:** Swarming growth on blood agar is a strong presumptive clue for *Proteus* species, which are oxidase negative like all Enterobacteriaceae. The oxidase test is still worth performing, because it costs seconds and it protects you against the one organism that swarming does not rule out. Pick from the edge of the swarm, not the center, where the film of growth is too thin to give a readable smear.\n- Oxidase test is used as a major characteristic for the identification of Gram-negative rods that are not in the *Enterobacteriaceae* family. Colonies suspected of belonging to other genera *Aeromonas, Pseudomonas, Neisseria, Campylobacter*, and *Pasteurella* are oxidase positive.\n- Gram-negative diplococci give a positive reaction. All members of the genus *Neisseria* are oxidase positive. *Moraxella spp*. that are either Gram-negative diplococci or coccobacilli are also oxidase-positive.\n\n## Complete Reference: Oxidase-Positive and Oxidase-Negative Organisms\n\n### Oxidase-positive organisms\n\n| Organism | Gram stain | Clinical significance |\n| --- | --- | --- |\n| *Pseudomonas aeruginosa* | Gram-negative rod | Nosocomial pneumonia, UTI, wound infections, cystic fibrosis; key distinction from Enterobacteriaceae |\n| *Pseudomonas fluorescens* | Gram-negative rod | Rare clinical significance; environmental contaminant; causes transfusion-associated septicemia |\n|  |  |  |\n| *Burkholderia cepacia* complex | Gram-negative rod | Important pathogen in cystic fibrosis; intrinsically resistant to aminoglycosides and polymyxins, usually susceptible to meropenem |\n| *Neisseria gonorrhoeae* | Gram-negative diplococci | Gonorrhea, PID, disseminated gonococcal infection |\n| *Neisseria meningitidis* | Gram-negative diplococci | Bacterial meningitis, meningococcemia |\n| *Moraxella catarrhalis* | Gram-negative diplococci | COPD exacerbations, otitis media, sinusitis |\n| *Haemophilus influenzae* | Gram-negative coccobacilli | Meningitis (type b), pneumonia, epiglottitis, otitis media |\n| *Campylobacter jejuni* | Gram-negative curved rod | Most common bacterial cause of gastroenteritis worldwide |\n| *Campylobacter coli* | Gram-negative curved rod | Gastroenteritis; similar presentation to *C. jejuni* |\n| *Helicobacter pylori* | Gram-negative curved rod | Peptic ulcer disease, gastric carcinoma; part of triple test (oxidase + urease + catalase all positive) |\n| *Vibrio cholerae* | Gram-negative curved rod | Cholera (rice-water diarrhea); important in outbreak investigation |\n| *Vibrio parahaemolyticus* | Gram-negative rod | Gastroenteritis associated with raw seafood |\n| *Vibrio vulnificus* | Gram-negative rod | Severe wound infection and septicemia from seawater exposure |\n| *Aeromonas hydrophila* | Gram-negative rod | Wound infections, diarrhea, septicemia in immunocompromised |\n| *Aeromonas caviae* | Gram-negative rod | Gastroenteritis, wound infections |\n| *Plesiomonas shigelloides* | Gram-negative rod | Diarrheal illness; associated with seafood and travel |\n| *Brucella* spp. | Gram-negative coccobacilli | Brucellosis (undulant fever); zoonotic infection |\n| *Pasteurella multocida* | Gram-negative coccobacilli | Wound infections from animal bites (dog, cat); bacteremia |\n| *Legionella pneumophila* | Gram-negative rod | Legionnaires' disease; weakly and variably oxidase positive, so the test has no diagnostic role here; does not grow on routine media and requires BCYE agar |\n| *Alcaligenes faecalis* | Gram-negative rod | Rare opportunistic infections; environmental organism |\n| *Bordetella pertussis* | Gram-negative coccobacilli | Whooping cough; laboratory diagnosis requires specific media and DFA |\n\n### Oxidase-negative organisms\n\n| Organism | Gram stain | Notes |\n| --- | --- | --- |\n| *Escherichia coli* | Gram-negative rod | Prototype oxidase-negative; UTI, diarrhea, septicemia |\n| *Klebsiella pneumoniae* | Gram-negative rod | Nosocomial pneumonia, UTI, bacteremia |\n| *Salmonella* spp. | Gram-negative rod | Typhoid fever, gastroenteritis, bacteremia |\n| *Shigella* spp. | Gram-negative rod | Bacillary dysentery |\n| *Proteus mirabilis* | Gram-negative rod | UTI, wound infections; swarming on blood agar |\n| *Enterobacter* spp. | Gram-negative rod | Nosocomial infections; AmpC beta-lactamase |\n| *Serratia marcescens* | Gram-negative rod | Nosocomial infections; red pigment at room temperature |\n| *Morganella morganii* | Gram-negative rod | Nosocomial UTI and wound infections |\n| *Yersinia* spp. | Gram-negative rod | *Y. enterocolitica* — gastroenteritis; *Y. pestis* — plague |\n| *Acinetobacter baumannii* | Gram-negative coccobacilli | The trap. A non-fermenting Gram-negative coccobacillus, so it looks like it should be oxidase positive. It is not. Oxidase-negative plus non-fermenting is the pairing that identifies it. |\n| *Stenotrophomonas maltophilia* | Gram-negative rod | The other trap. Non-fermenter, oxidase negative. Distinguished from Acinetobacter by DNase production and maltose oxidation. |\n| *Staphylococcus* spp. | Gram-positive cocci | Oxidase-negative ([use modified oxidase\u002Fmicrodase test to differentiate from Micrococcus](https:\u002F\u002Fmicrobeonline.com\u002Fmodified-oxidase-test-microdase-principle-procedure-uses\u002F)) |\n| *Streptococcus* spp. | Gram-positive cocci | Oxidase-negative |\n| *Enterococcus* spp. | Gram-positive cocci | Oxidase-negative |\n\n### The exceptions that matter for exams\n\nThree organisms break the pattern students are taught, and examiners know it.\n\n- **Acinetobacter baumannii** — non-fermenter, but oxidase **negative**.\n- **Stenotrophomonas maltophilia** — non-fermenter, but oxidase **negative**.\n- **Vibrio metschnikovii** — a *Vibrio*, but oxidase **negative**. The genus rule has an exception, and this is it.\n\nNote what the first two have in common. If you have been taught \"oxidase positive means non-fermenter,\" you have been taught the converse of a true statement. The true statement is: **oxidase positive rules out Enterobacteriaceae.** It does not rule in non-fermenters, and oxidase negative does not rule them out.\n\n## Clinical Identification Workflow — How the Oxidase Test Is Used\n\nThe oxidase test is one of the first tests performed on gram-negative organisms and immediately divides them into two major groups:\n\n### Gram-negative organism identification- decision pathway\n\n```\nGRAM-NEGATIVE ORGANISM\n│\n├── OXIDASE POSITIVE → Not Enterobacteriaceae\n│   │\n│   ├── Cocci or diplococci → Neisseria spp., Moraxella catarrhalis\n│   │   └── Further: sugar fermentation, superoxol test\n│   │\n│   ├── Coccobacilli → Haemophilus, Brucella, Bordetella, Pasteurella, Francisella\n│   │   └── Further: X and V factor requirements, growth characteristics\n│   │\n│   ├── Curved rods → Campylobacter, Helicobacter, Vibrio\n│   │   └── Further: oxidative-fermentative test, growth temperature, microaerophily\n│   │\n│   └── Straight rods (non-fermenter) → Pseudomonas, Burkholderia, Alcaligenes\n│       └── Further: O-F test, pigment, cetrimide agar, motility\n│\n└── OXIDASE NEGATIVE → Likely Enterobacteriaceae (or Acinetobacter \u002F Stenotrophomonas)\n    │\n    ├── Fermenter (O-F positive) → Enterobacteriaceae\n    │   └── Further: TSI, SIM, urease, citrate, IMViC battery\n    │\n    └── Non-fermenter (O-F negative\u002Falkaline) → Acinetobacter, Stenotrophomonas\n        └── Further: growth at 44°C (A. baumannii), DNase and maltose oxidation (S. maltophilia)\n```\n\n### Three clinically important oxidase-positive identifications\n\n**1. [Pseudomonas aeruginosa](https:\u002F\u002Fmicrobeonline.com\u002Fpseudomonas-aeruginosa-properties-pathogenesis-and-diagnosis\u002F):** Oxidase positive + non-fermenter on [O-F test](https:\u002F\u002Fmicrobeonline.com\u002Foxidative-fermentative-test-principle-procedure-results\u002F) + blue-green pyocyanin pigment + fruity grape-like odor + growth on cetrimide agar = presumptive *P. aeruginosa*. Confirmed by MALDI-TOF or biochemical panel.\n\n**2. [Neisseria gonorrhoeae](https:\u002F\u002Fmicrobeonline.com\u002Fneisseria-gonorrhoeae-properties-disease-pathogenesis-and-laboratory-diagnosis\u002F):** Gram-negative intracellular diplococci from urethral\u002Fcervical discharge + oxidase positive + glucose fermentation only (not maltose) = presumptive *N. gonorrhoeae*. *N. meningitidis* ferments both glucose and maltose.\n\n**3. [Campylobacter jejuni](https:\u002F\u002Fmicrobeonline.com\u002Fcampylobacter-jejuni-disease-properties-and-laboratory-diagnosis\u002F):** Oxidase positive + gram-negative curved rod + growth at 42°C in microaerophilic conditions + hippurate positive = *C. jejuni*. Hippurate-negative oxidase-positive curved rods suggest *C. coli*.\n\n## Quality Control\n\nBacterial species showing positive and negative reactions should be run as controls at frequent intervals.\n\nThe following are suggested:\n\n- Oxidase positive: *Pseudomonas aeruginosa* ATCC 27853\n- Oxidase negative: *Escherichia coli* ATCC 25922\n\n## Precautions and Limitations\n\n- Timing is critical to accurate testing.\n- Use fresh reagents, no older than 1 week, older reagents can autooxidize thus giving erroneous results. Do not use if the reagent or filter paper is purple.\n- Do not test organisms growing on media that contain glucose or dyes (e.g., MacConkey agar or [EMB agar](\u002Feosin-methylene-blue-emb-agar-composition-uses-colony-characteristics\u002F)).\n- Do not use nickel-base alloy wires containing chromium and iron (nichrome) to pick the colony and make a smear as this may give false-positive results.\n- Bacteria grown on media-containing dyes may give aberrant results.\n- Older cultures are less metabolically active so may give false-negative results within the mentioned observation time.\n\n> The oxidase test must be performed from 5% sheep blood agar or another medium without fermentable sugar. Fermentation of carbohydrates results in acidification of the medium (e.g., lactose in MacConkey Agar or Sucrose in TCBS), and a false negative oxidase test may result if the surrounding pH is below 5.1. Subinoculation on nutrient agar is required before the oxidase test can be performed. During the identification of suspected Vibrio cholerae isolate, it is not possible to perform an oxidase test directly from a TCBS culture because the acid produced by the sucrose fermenting colonies will inhibit the oxidase reaction.\n\n### How to remember\n\n> Mnemonics for oxidase positive organisms-PVNCH (It’s just an acronym inspired by the famous mnemonic for urease positive organisms-PUNCH)\n\n**PVNCH, and why it is not enough**\n\nThe five you will be asked for first:\n\n- **P** — *Pseudomonas*\n- **V** — *Vibrio*\n- **N** — *Neisseria*\n- **C** — *Campylobacter*\n- **H** — *Helicobacter* and *Haemophilus*\n\nThis mnemonic is deliberately incomplete. It covers the Gram-negative rods and cocci you will meet on a ward. It leaves out *Aeromonas*, *Plesiomonas*, *Moraxella*, *Pasteurella*, *Brucella*, *Bordetella*, and *Alcaligenes*. If you find yourself reaching for PVNCH and the organism is not in it, that is the mnemonic working correctly. It is telling you the answer is one of the environmental or zoonotic organisms, and those are worth learning by name.\n\n**The gate, not the fork**\n\nPicture the oxidase reagent as a gate with a guard who only accepts a ticket handed over by cytochrome c. Pseudomonas walks up holding that ticket. E. coli arrives holding a different ticket, one issued upstream at the quinone pool, and the guard cannot read it. E. coli is not turned away from respiring. It is turned away from *this particular door*.\n\nAsk yourself, before you look anything up: *if E. coli respires aerobically, why is it oxidase negative?* If you can answer that in one sentence, you understand this test. If you cannot, reread the branched respiratory chain section. Everything else in the article is downstream of it.\n\n## Key exam facts in one table\n\n| Question | Answer | The reason behind it |\n| --- | --- | --- |\n| What enzyme is detected? | Cytochrome c oxidase, also called cytochrome aa3 or complex IV | It is the terminal oxidase that accepts electrons from cytochrome c |\n| What is the reagent? | 1% TMPD (tetramethyl-p-phenylenediamine dihydrochloride), Kovács reagent | TMPD is an artificial electron donor that enters the chain at cytochrome c |\n| What is the positive result? | Purple within 10 seconds | TMPD is oxidized to indophenol blue |\n| What is a delayed positive? | Purple at 60 to 90 seconds | Slow or aged culture, or genuinely slow organisms such as some *Pasteurella* |\n| Color after 2 minutes? | Negative. This is reagent autooxidation, not the organism | Air oxidizes TMPD on its own; a blank paper will do the same |\n| Which family is uniformly negative? | Enterobacteriaceae, all members | They terminate in quinol oxidases (cytochrome bo3, bd-I), upstream of where TMPD donates |\n| Does negative mean anaerobe? | No | *E. coli* is a facultative anaerobe that respires aerobically and is oxidase negative |\n| Five to name fast | Pseudomonas, Vibrio, Neisseria, Campylobacter, Helicobacter — **PVNCH** | The clinically commonest positives |\n| The two non-fermenter traps | *Acinetobacter baumannii*, *Stenotrophomonas maltophilia* — both oxidase **negative** | Oxidase positive rules out Enterobacteriaceae. It does not rule in non-fermenters |\n| The genus exception | *Vibrio metschnikovii* is oxidase negative | Genus-level rules in microbiology almost always have one |\n| Why never test from MacConkey or TCBS? | Sugar fermentation drops local pH below 5.1 and the reaction cannot proceed | Gives a **false negative** on a truly positive organism |\n| Correct medium to test from | Nutrient agar, trypticase soy agar, or 5% sheep blood agar | No fermentable sugar, no dyes |\n| Why not a nichrome loop? | Nickel and iron oxidize TMPD directly | Gives a **false positive** with no organism involved |\n| Acceptable transfer tools | Platinum loop, wooden applicator stick, sterile plastic loop, glass rod, sterile toothpick, sterile swab | All are inert toward TMPD |\n| Culture age? | 18 to 24 hours | Older colonies are metabolically slow and read false negative |\n| Reagent shelf life | 1 week, refrigerated, in a dark bottle | Autooxidation. Discard if the reagent or paper has turned purple |\n| Positive QC organism | *Pseudomonas aeruginosa* | Rapid, unambiguous purple |\n| Negative QC organism | *Escherichia coli* | Prototype Enterobacteriaceae |\n| Where does oxidase sit in the workflow? | First, before TSI, SIM, urease, citrate | A positive result removes the organism from the Enterobacteriaceae and redirects the entire panel |\n\n### Where students get confused\n\n**\"Oxidase negative means the organism is anaerobic.\"** It does not. *E. coli* respires aerobically and is oxidase negative. The test asks whether the chain terminates in cytochrome c oxidase, not whether the organism uses oxygen. This is the single most common misconception about this test and it survives into postgraduate exams.\n\n**\"Oxidase positive means non-fermenter.\"** The converse of a true statement is not a true statement. Oxidase positive rules **out** Enterobacteriaceae. *Vibrio* and *Aeromonas* are oxidase positive and are fermenters. *Acinetobacter* and *Stenotrophomonas* are non-fermenters and are oxidase negative. Use the O-F test to establish fermentation, not the oxidase test.\n\n**Testing straight from MacConkey, EMB, or TCBS.** The most consequential error on this list. A lactose fermenter on MacConkey or a sucrose fermenter on TCBS acidifies its own surroundings. Below pH 5.1 the reaction is chemically blocked. You will call a *Vibrio* negative. Always subculture to nutrient agar or blood agar first.\n\n**Using a nichrome loop.** The nickel and iron in the alloy oxidize TMPD without any enzyme present. You will get a purple that means nothing. Platinum, wood, or plastic only. Notice that this error and the previous one push in **opposite directions**: the wrong medium gives you a false negative, the wrong loop gives you a false positive. Students often remember that both are forbidden and forget which does what.\n\n**Waiting too long.** Read at 10 seconds. Read again at 90. Stop. Anything that appears after 2 minutes is the reagent reacting with air, and it will appear on a blank paper too. If you are unsure, run a reagent-only control alongside. This takes 5 seconds and settles the question permanently.\n\n**Reading a purple reagent bottle as a good sign.** If the Kovács reagent or the impregnated paper is already purple before the organism touches it, the reagent has autooxidized. It is dead. Discard it. Reagent that has been left on the bench in daylight will do this within a day.\n\n**Confusing the catalase and oxidase tests.** They are both rapid, both enzyme tests, both done early. Beyond that they share nothing. Catalase separates *Staphylococcus* from *Streptococcus* using hydrogen peroxide, and a nichrome loop is fine. Oxidase separates non-Enterobacteriaceae from Enterobacteriaceae using TMPD, and a nichrome loop ruins it. If you remember one distinction, remember the loop.\n\n**Testing a swarming Proteus and skipping the confirmation.** Swarming is a strong clue, not a result. Pick from the edge of the swarm where the growth is thick enough to smear, and run the test. It takes seconds and it protects you.\n\n**References and further readings**\n\n1. Kovács N. Identification of *Pseudomonas pyocyanea* by the oxidase reaction. *Nature.* 1956;178(4535):703. doi:10.1038\u002F178703a0\n2. Shields P, Cathcart L. Oxidase test protocol. American Society for Microbiology, 2010 (updated 2017).\n3. Leber AL, editor. *Clinical Microbiology Procedures Handbook.* 4th ed. Washington, DC: ASM Press; 2016. doi:10.1128\u002F9781555818814\n4. Procop GW, Church DL, Hall GS, Janda WM, Koneman EW, Schreckenberger PC, Woods GL. *Koneman's Color Atlas and Textbook of Diagnostic Microbiology.* 7th ed. Philadelphia: Wolters Kluwer; 2017.\n5. Tille PM. *Bailey and Scott's Diagnostic Microbiology.* 15th ed. St. Louis: Elsevier; 2022.\n6. World Health Organization. *Laboratory Methods for the Diagnosis of Epidemic Dysentery and Cholera.* Geneva: WHO; 1999.\n7. Borisov VB, Gennis RB, Hemp J, Verkhovsky MI. The cytochrome bd respiratory oxygen reductases. *Biochim Biophys Acta.* 2011;1807(11):1398-1413. doi:10.1016\u002Fj.bbabio.2011.06.016",[52,55,58,61,64,67,70,73],{"question":53,"answer":54},"What does a positive oxidase test indicate?","\u003Cp>Presence of cytochrome c oxidase in the electron transport chain. Does NOT mean the organism is a strict aerobe, \u003Cem>Vibrio cholerae \u003C\u002Fem>and \u003Cem>Campylobacter \u003C\u002Fem>are oxidase-positive but not strict aerobes. A positive result immediately excludes the Enterobacteriaceae family, which are all oxidase-negative.\u003C\u002Fp>",{"question":56,"answer":57},"Why are Enterobacteriaceae oxidase-negative?","\u003Cp>They lack cytochrome c oxidase, using other terminal oxidases (cytochrome bd, cytochrome bo) that do not react with TMPD reagent. Absence of cytochrome c oxidase is a defining characteristic of the entire Enterobacteriaceae family, making the oxidase test one of the most powerful single tests for separating gram-negative rods.\u003C\u002Fp>",{"question":59,"answer":60},"Why must the oxidase test not be performed from MacConkey agar?","A lactose-fermenting colony on MacConkey acidifies its immediate surroundings. Below roughly pH 5.1 the cytochrome c oxidase reaction cannot proceed, so a truly oxidase-positive organism reads negative. The dyes in MacConkey and EMB can also obscure color development. The error is a false negative, not a false positive. Always subculture to nutrient agar, blood agar, or tryptic soy agar first.",{"question":62,"answer":63},"Why does a nichrome wire give a false-positive oxidase result?","Nickel and iron in nichrome oxidize TMPD directly, producing the same purple endpoint that the enzyme would, but with no enzyme involved at all. The result looks identical and means nothing. Always use a platinum loop, wooden applicator stick, or plastic loop.",{"question":65,"answer":66},"What is the difference between the standard and modified oxidase (Microdase) test?","\u003Cp>Standard oxidase test: TMPD reagent applied to gram-negative organisms, differentiates Enterobacteriaceae from non-fermenters. Modified oxidase (Microdase): TMPD in DMSO applied to gram-positive cocci, differentiates \u003Cem>Micrococcus\u003C\u002Fem> (positive) from\u003Cem> Staphylococcus \u003C\u002Fem>(negative). Standard reagent gives unreliable results with gram-positive cocci.\u003C\u002Fp>",{"question":68,"answer":69},"Why is timing critical in the oxidase test?","TMPD undergoes spontaneous auto-oxidation in air, turning purple without any bacterial enzyme activity. Purple within 10 seconds is a true positive. Purple at 60 to 90 seconds is reported as a delayed positive. Color appearing after 2 minutes is auto-oxidation, not a result, and a reagent-only blank paper will develop the same color. Do not interpret anything after 2 minutes.",{"question":71,"answer":72},"Is Acinetobacter oxidase-positive or negative?","\u003Cp>Oxidase-NEGATIVE, an important exception among non-fermenting gram-negative rods. \u003Cem>Pseudomonas aeruginosa\u003C\u002Fem> (the other major non-fermenter) is oxidase-positive. \u003Cem>Acinetobacter\u003C\u002Fem> oxidase-negative vs \u003Cem>Pseudomonas\u003C\u002Fem> oxidase-positive is one of the key distinguishing tests between these two MDR nosocomial pathogens.\u003C\u002Fp>",{"question":74,"answer":75},"What quality control organisms are recommended for the oxidase test?","\u003Cp>\u003Cem>Pseudomonas aeruginosa\u003C\u002Fem> ATCC 27853 (positive control, dark purple within 10 seconds) and \u003Cem>Escherichia coli \u003C\u002Fem>ATCC 25922 (negative control, remains colorless). If either control fails, discard the reagent batch, prepare fresh, and repeat controls before reporting patient results.\u003C\u002Fp>",[77],"enzyme-tests",[79,113,147,180,202,228,238,271],{"slug":80,"title":81,"description":82,"seoTitle":49,"seoDescription":49,"author":44,"createdDate":83,"lastUpdatedDate":84,"draft":47,"category":48,"image":49,"faq":85,"tags":110},"triple-sugar-iron-agar-tsi-principle-procedure-and-interpretation","Triple Sugar Iron (TSI) Agar: Principle, Results, and Interpretation","\u003Cp>TSI agar: principle, composition, procedure, and complete interpretation guide: all possible slant\u002Fbutt combinations with organisms, H₂S production, gas formation, and comparison with KIA.\u003C\u002Fp>","2013-07-16","2026-08-24",[86,89,92,95,98,101,104,107],{"question":87,"answer":88},"What does K\u002FA mean in TSI results?","\u003Cp>Alkaline slant (red) \u002F Acid butt (yellow). Glucose-only fermentation, lactose and sucrose not fermented. Classic pattern of \u003Cem>Salmonella\u003C\u002Fem> and \u003Cem>Shigella.\u003C\u002Fem>\u003C\u002Fp>",{"question":90,"answer":91},"What does A\u002FA mean in TSI?","\u003Cp>Acid slant \u002F Acid butt, both yellow. Lactose and\u002For sucrose fermented in addition to glucose. Classic pattern of \u003Cem>E. coli, Klebsiella\u003C\u002Fem>, and \u003Cem>Enterobacter.\u003C\u002Fem>\u003C\u002Fp>",{"question":93,"answer":94},"\u003Cp>How do you differentiate \u003Cem>S\u003C\u002Fem>. Typhi from other \u003Cem>Salmonella\u003C\u002Fem> on TSI?\u003C\u002Fp>","\u003Cp>\u003Cem>S\u003C\u002Fem>. Typhi: K\u002FA + H2S (variable) + NO GAS. Other \u003Cem>Salmonella:\u003C\u002Fem> K\u002FA + strong H₂S + strong gas. No gas production is the key distinguishing feature of S. Typhi.\u003C\u002Fp>",{"question":96,"answer":97},"\u003Cp>Why does \u003Cem>Shigella\u003C\u002Fem> give K\u002FA without H₂S or gas?\u003C\u002Fp>","\u003Cp>Ferments only glucose; lacks thiosulfate reductase (no H₂S) and formate hydrogen lyase (no gas). K\u002FA + no H2S + no gas + non-motile = highly suspicious for \u003Cem>Shigella.\u003C\u002Fem>\u003C\u002Fp>",{"question":99,"answer":100},"Why must TSI be read at exactly 18-24 hours?","Early: insufficient acid. Late: organisms ferment trace sugars giving false A\u002FA. Non-fermenters may revert butt to alkaline. The 18-24 hour window is the only reliable reading time.",{"question":102,"answer":103},"\u003Cp>What does H₂S in TSI indicate?\u003C\u002Fp>","\u003Cp>Black ferrous sulfide = H₂S production. Strong: \u003Cem>Salmonella, Proteus\u003C\u002Fem>. Moderate: \u003Cem>Citrobacter freundii\u003C\u002Fem>. Variable: \u003Cem>S\u003C\u002Fem>. Typhi. H₂S only forms in acidic butt, K\u002FK results cannot show black precipitate.\u003C\u002Fp>",{"question":105,"answer":106},"What is the difference between TSI and KIA?","\u003Cp>TSI: glucose + lactose + sucrose. KIA: glucose + lactose only, no sucrose. Sucrose fermenters (\u003Cem>V. cholerae\u003C\u002Fem>) give A\u002FA on TSI but K\u002FA on KIA, potentially confused with Salmonella on KIA.\u003C\u002Fp>",{"question":108,"answer":109},"When is TSI used vs SIM medium?","\u003Cp>Always inoculated together. TSI: carbohydrate fermentation + H₂S+ gas. SIM: H₂S + indole + motility. Together they identify most clinically important Enterobacteriaceae.\u003C\u002Fp>",[111,112],"carbohydrate-utilization","h2s-production",{"slug":114,"title":115,"description":116,"seoTitle":117,"seoDescription":118,"author":44,"createdDate":119,"lastUpdatedDate":120,"draft":47,"category":48,"image":49,"faq":121,"tags":146},"catalase-test-principle-uses-procedure-results","Catalase Test: The 3-Second Test That Separates Staph from Strep, and Five Ways It Lies","\u003Cp>Bubbles in 3 seconds means \u003Cem>Staphylococcus\u003C\u002Fem>. But red blood cells bubble, nichrome loops bubble, and enterococci grown on blood agar bubble weakly. Learn what the catalase test actually detects, why streptococci cannot make the enzyme, and how to tell a true positive from the four things that imitate one.\u003C\u002Fp>","Catalase Test: Procedure, Controls, False Results, and Interpretation","Run and interpret the catalase test with proper controls, distinguish staphylococci from streptococci, and avoid blood agar and loop-related false results.","2013-10-07","2026-08-16",[122,125,128,131,134,137,140,143],{"question":123,"answer":124},"What is the principle of the catalase test?","The catalase test detects the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen. Visible bubbling indicates a positive result. Reaction: 2H₂O₂ → 2H₂O + O₂.",{"question":126,"answer":127},"Why is the catalase test important in clinical microbiology?","\u003Cp>It separates \u003Cem>Staphylococcus\u003C\u002Fem> (catalase-positive) from \u003Cem>Streptococcus\u003C\u002Fem> and \u003Cem>Enterococcus \u003C\u002Fem>(catalase-negative), guiding further identification. It also helps identify \u003Cem>Mycobacterium tuberculosis\u003C\u002Fem> and differentiate \u003Cem>Bacillus\u003C\u002Fem> from \u003Cem>Clostridium.\u003C\u002Fem>\u003C\u002Fp>",{"question":129,"answer":130},"What causes a false positive in the catalase test?","False positives are caused by using metal loops (which non-enzymatically decompose H₂O₂), carrying over red blood cells from blood agar, or testing on Mueller-Hinton agar.",{"question":132,"answer":133},"What causes a false negative in the catalase test?","The most common cause is using colonies older than 24 hours. Catalase production is highest during logarithmic growth; older cultures produce less enzyme, leading to insufficient bubbling.",{"question":135,"answer":136},"What is the difference between the slide and tube catalase test?","The slide test is quicker but risks RBC carryover from blood agar. The tube test is preferred for blood agar cultures as it reduces false positive risk.",{"question":138,"answer":139},"Why should you not use a metal loop in the catalase test?","Metal loops non-enzymatically decompose H₂O₂, producing bubbles that mimic a true positive result. Use a platinum loop, wooden stick, or plastic loop instead.",{"question":141,"answer":142},"\u003Cp>Are all \u003Cem>Staphylococcu\u003C\u002Fem>s species catalase positive?\u003C\u002Fp>","\u003Cp>Almost all \u003Cem>Staphylococcus\u003C\u002Fem> species are catalase positive, distinguishing them from \u003Cem>Streptococcus\u003C\u002Fem> and \u003Cem>Enterococcus.\u003C\u002Fem> Rare catalase-negative staphylococcal strains exist, so results should be interpreted with other tests.\u003C\u002Fp>",{"question":144,"answer":145},"What is pseudocatalase and which bacteria produce it?","\u003Cp>Pseudocatalase is a cytochrome-based mechanism in some \u003Cem>Enterococcus\u003C\u002Fem> and \u003Cem>Lactobacillus\u003C\u002Fem> strains that weakly decomposes H₂O₂, producing delayed weak bubbling after 20-30 seconds unlike the immediate vigorous bubbling of true catalase-positive organisms.\u003C\u002Fp>",[77],{"slug":148,"title":149,"description":150,"seoTitle":49,"seoDescription":49,"author":44,"createdDate":151,"lastUpdatedDate":152,"draft":47,"category":153,"image":49,"faq":154,"tags":179},"tryptic-soy-agar-tsa-composition-preparation-uses","Tryptic Soy Agar (TSA): Composition, Preparation, Uses, and Colony Morphology","Tryptic Soy Agar (TSA) is the most widely used general-purpose medium in clinical microbiology. Learn its composition, preparation, uses including blood culture and McFarland suspension, colony morphology, and how it differs from nutrient agar.","2018-02-09","2026-08-03","culture-media",[155,158,161,164,167,170,173,176],{"question":156,"answer":157},"What is the difference between tryptic soy agar and nutrient agar?","Both are general-purpose, non-selective, non-differential media, but they differ in nitrogen source. TSA uses pancreatic digest of casein plus peptic digest of soybean meal, giving a more complete amino acid profile. Nutrient agar uses beef extract and peptone, which is simpler and less nutritionally complete. TSA supports a wider range of organisms, including moderately fastidious ones, and is standard in clinical laboratories. Nutrient agar remains common in environmental, food, and teaching microbiology because it is cheaper.",{"question":159,"answer":160},"Is tryptic soy agar selective or differential?","Neither. TSA contains no inhibitory agents and no indicator systems. It is a general-purpose enriched medium, which is why it is used for subculture, pure culture preparation, and colony maintenance rather than for primary isolation from mixed specimens.",{"question":162,"answer":163},"What is the difference between TSA and TSB?","Composition is identical apart from agar. TSB is the broth form, prepared at 30 g\u002FL rather than 40 g\u002FL because it omits the 15 g of agar and adjusts slightly. TSB is used where a liquid is needed: blood culture bottles, inoculum standardization against the 0.5 McFarland standard, and broth dilution methods. TSA is used where colonies must be isolated and examined.",{"question":165,"answer":166},"Why is tryptic soy agar used as a blood agar base?","Because it is nutritionally rich enough to support most clinically significant bacteria on its own, chemically neutral with no inhibitors or indicators that would interfere with reading hemolysis, and it accepts 5% sheep blood cleanly at 50°C. The base grows the organism; the blood makes hemolysis visible and supports fastidious species. Columbia agar base is the other commonly used blood agar base.",{"question":168,"answer":169},"Why must TSA be cooled to 50°C before adding blood?","Above roughly 50°C the red cells lyse, which destroys the hemolysis patterns the plate exists to show and turns the medium brown. Below about 45°C the agar begins to set before the blood is mixed and poured, giving uneven plates. The narrow window around 50°C is the reason blood agar preparation uses a water bath rather than bench cooling.",{"question":171,"answer":172},"Can tryptic soy agar be used for antimicrobial susceptibility testing?","Not as the standard testing medium. CLSI specifies Mueller-Hinton agar for routine disc diffusion, and Mueller-Hinton with 5% defibrinated sheep blood for streptococci. TSA's role is upstream but constant: the pure subculture that provides the test isolate, and the TSB used to standardize the inoculum to 0.5 McFarland.",{"question":174,"answer":175},"What is soybean casein digest medium?","The same medium as tryptic soy agar. SCDM, Casein Soy Peptone Agar, and Trypticase Soy Agar are alternative names for the identical formulation. The term SCDM appears frequently in pharmacopoeial and sterility-testing contexts.",{"question":177,"answer":178},"How long can TSA plates be stored?","Poured plates keep for two to four weeks at 2 to 8°C when stored inverted in sealed bags to limit moisture loss. Plates showing dehydration, cracking, contamination, or color change should be discarded. Always allow plates to reach room temperature before inoculating, since condensation on a cold surface spreads the inoculum.",[],{"slug":181,"title":182,"description":183,"seoTitle":49,"seoDescription":49,"author":44,"createdDate":184,"lastUpdatedDate":46,"draft":47,"category":48,"image":49,"faq":185,"tags":201},"modified-oxidase-test-microdase-principle-procedure-uses","Modified Oxidase (Microdase) Test: The DMSO Trick That Separates Micrococcus From Staphylococcus","The standard oxidase reagent fails on Gram-positive cocci, so the microdase test dissolves it in DMSO to reach the cytochrome c inside. A blue disk means Micrococcus (which has cytochrome c); no color means Staphylococcus (which usually does not). Here is why DMSO matters, the mechanism, and the Staphylococcus sciuri exception that breaks the rule.","2015-10-30",[186,189,192,195,198],{"question":187,"answer":188},"What is the difference between the oxidase test and the modified oxidase (microdase) test?","They detect the same enzyme, cytochrome c oxidase, but are used on different organisms and with a different reagent solvent. The standard oxidase test uses a water-based reagent on Gram-negative rods, for example to separate Enterobacteriaceae from non-fermenters. The modified oxidase (microdase) test dissolves the reagent in DMSO so it can penetrate the thick cell walls of Gram-positive cocci, and it is used to separate Micrococcus (positive) from Staphylococcus (negative). Without the DMSO modification, the standard reagent gives unreliable results on Gram-positive cocci.",{"question":190,"answer":191},"Why is DMSO used in the microdase test?","Because the standard oxidase reagent cannot reliably reach the cytochrome c inside Gram-positive cocci; their cell walls block the water-based reagent, giving weak or false results. Dimethyl sulfoxide (DMSO) is a penetrating solvent that makes the cells permeable, carrying the reagent through the cell wall to the cytochrome, and it also stabilizes the reagent against auto-oxidation. Dissolving the reagent in DMSO instead of water is the single change that defines the modified oxidase test.",{"question":193,"answer":194},"What does a positive microdase test indicate?","A blue or purple-blue color on the disk within two minutes indicates the organism has cytochrome c oxidase, which among catalase-positive Gram-positive cocci points to Micrococcus. Staphylococcus usually lacks cytochrome c and gives no color change. The exceptions are Staphylococcus sciuri, S. lentus, and S. vitulinus, which carry c-type cytochromes and give a positive result despite being staphylococci.",{"question":196,"answer":197},"Which staphylococci give a positive microdase test?","Most staphylococci are microdase negative, but three species are exceptions: Staphylococcus sciuri, S. lentus, and S. vitulinus. These carry c-type cytochromes and produce a positive blue reaction, breaking the general rule that a positive microdase means Micrococcus. Because of these exceptions, a positive result should be interpreted alongside other tests such as bacitracin, furazolidone, or lysostaphin susceptibility.",{"question":199,"answer":200},"Why must the microdase test be read within 2 minutes?","Because the reagent, tetramethyl-p-phenylenediamine, spontaneously oxidizes in air and turns blue on its own over time. A color that develops after two minutes may be this auto-oxidation rather than true bacterial enzyme activity, giving a false positive. Reading and recording the result within two minutes ensures the blue color reflects the organism's cytochrome c oxidase, not the reagent aging.",[77],{"slug":203,"title":204,"description":205,"seoTitle":49,"seoDescription":49,"author":44,"createdDate":206,"lastUpdatedDate":207,"draft":47,"category":48,"image":49,"faq":208,"tags":227},"oxidative-fermentative-test-principle-procedure-results","OF Test: Fermenter or Non-Fermenter? The Two-Tube Test That Identifies Pseudomonas","\u003Cp>When the oxidase test flags an oxidase-positive Gram-negative rod, the next question is whether it ferments glucose or only oxidizes it. The OF test answers that with two tubes, one sealed from air. Oxidative plus oxidase-positive points to \u003Cem>Pseudomonas.\u003C\u002Fem> Here is the low-peptone mechanism, the paired-tube reading logic, and why weak oxidative acid needs a special medium to detect.\u003C\u002Fp>","2016-02-11","2026-08-25",[209,212,215,218,221,224],{"question":210,"answer":211},"What is the difference between oxidative and fermentative metabolism in the OF test?","Fermentative organisms produce acid from glucose whether or not oxygen is present, so both the open tube and the oil-sealed tube turn yellow. Oxidative organisms produce acid from glucose only when oxygen is present, so only the open tube turns yellow while the sealed tube stays green. The sealed tube is the key: since it has no oxygen, acid there can only come from fermentation. Acid in the sealed tube means fermenter; acid only in the open tube means oxidizer.",{"question":213,"answer":214},"Why does OF medium contain so little peptone?","Because oxidative organisms produce only a tiny amount of weak acid, and in a peptone-rich medium that acid is neutralized by alkaline amines released as the organism breaks down the peptone. Hugh and Leifson reduced the peptone to about 0.2% so there are far fewer alkaline amines, letting the weak acid lower the pH enough for the bromothymol blue indicator to detect it. The high glucose concentration, about 1%, further increases the acid produced. This low-peptone, high-glucose design is the entire reason OF medium works where an ordinary sugar tube fails.",{"question":216,"answer":217},"Why are two tubes used in the OF test?","To compare the organism's metabolism with and without oxygen. One tube is left open to the air (aerobic) and the other is sealed under a layer of mineral oil (anaerobic). Neither tube is meaningful alone; the pattern across both gives the result. Both yellow means fermentative, open-only yellow means oxidative, and neither yellow means nonsaccharolytic.",{"question":219,"answer":220},"\u003Cp>How does the OF test help identify \u003Cem>Pseudomonas aeruginosa?\u003C\u002Fem>\u003C\u002Fp>","\u003Cp>\u003Cem>Pseudomonas aeruginosa \u003C\u002Fem>is a non-fermenter: it oxidizes glucose but cannot ferment it, giving an oxidative OF result (open tube yellow, sealed tube green). Combined with a positive oxidase test, an oxidative OF result on a Gram-negative rod is the presumptive signature of Pseudomonas, especially alongside blue-green pigment, a grape-like odor, and growth at 42 degrees. The OF and oxidase tests together are the backbone of non-fermenter identification.\u003C\u002Fp>",{"question":222,"answer":223},"What does a nonsaccharolytic result look like?","\u003Cp>Neither tube turns yellow, because the organism does not use glucose at all. The open tube may actually turn blue, more alkaline than the starting green, because the organism is breaking down peptone and releasing alkaline amines. \u003Cem>Alcaligenes faecalis \u003C\u002Fem>is a classic example. The blue color is a protein-metabolism reaction, not a sugar reaction.\u003C\u002Fp>",{"question":225,"answer":226},"Which non-fermenters are oxidase-negative?","\u003Cp>\u003Cem>Acinetobacter baumannii\u003C\u002Fem> and \u003Cem>Stenotrophomonas maltophilia \u003C\u002Fem>are the two important non-fermenters that are oxidase-negative, which makes them exceptions to the common shortcut that oxidase-positive means non-fermenter. They give oxidative or nonsaccharolytic OF results while being oxidase-negative, so the OF and oxidase tests must be read together to place them correctly.\u003C\u002Fp>",[],{"slug":229,"title":230,"description":231,"seoTitle":49,"seoDescription":49,"author":44,"createdDate":232,"lastUpdatedDate":233,"draft":47,"category":234,"image":49,"faq":235,"tags":236},"neisseria-gonorrhoeae-properties-disease-pathogenesis-and-laboratory-diagnosis","Neisseria gonorrhoeae: Properties, Pathogenesis, Virulence Factors, and Lab Diagnosis","\u003Cp>\u003Cem>Neisseria gonorrhoeae\u003C\u002Fem> causes gonorrhoea: the second most common STI globally. Learn its Gram-negative diplococcus properties, virulence factors (pili, Opa proteins, IgA protease, LOS, PorB), diseases (urethritis, PID, ophthalmia neonatorum), lab diagnosis (Gram stain, culture, NAAT), and AMR resistance timeline.\u003C\u002Fp>","2013-06-10","2026-08-06","bacteriology",[],[237],"gram-negative-cocci",{"slug":239,"title":240,"description":241,"seoTitle":49,"seoDescription":49,"author":44,"createdDate":242,"lastUpdatedDate":243,"draft":47,"category":234,"image":49,"faq":244,"tags":269},"campylobacter-jejuni-disease-properties-and-laboratory-diagnosis","Campylobacter jejuni: Gastroenteritis, Guillain-Barré Syndrome, and Laboratory Diagnosis","\u003Cp>How \u003Cem>Campylobacter jejuni \u003C\u002Fem>causes the world's most common bacterial gastroenteritis, its link to Guillain-Barré syndrome, and how the laboratory identifies it (curved rods, 42°C, microaerophilic, oxidase positive).\u003C\u002Fp>","2013-05-18","2026-08-13",[245,248,251,254,257,260,263,266],{"question":246,"answer":247},"\u003Cp>What is the most common bacterial cause of gastroenteritis worldwide?\u003C\u002Fp>","\u003Cp>\u003Cem>Campylobacter jejuni\u003C\u002Fem>. It usually causes bloody, foul-smelling, self-limited diarrhea, most often from undercooked poultry.\u003C\u002Fp>",{"question":249,"answer":250},"\u003Cp>At what temperature does Campylobacter jejuni grow?\u003C\u002Fp>","\u003Cp>Best at 42°C, which is higher than body temperature. Laboratories use this to select for it, incubating stool cultures at 42°C in a low-oxygen atmosphere. The related species \u003Cem>C. fetus\u003C\u002Fem> grows at 25°C instead.\u003C\u002Fp>",{"question":252,"answer":253},"\u003Cp>Why does Campylobacter need a special atmosphere to grow?\u003C\u002Fp>","\u003Cp>Because it is microaerophilic: it grows best in about 5% oxygen with added carbon dioxide, not in ordinary room air. It will not grow on a standard aerobic plate.\u003C\u002Fp>",{"question":255,"answer":256},"\u003Cp>How does Campylobacter cause Guillain-Barré syndrome?\u003C\u002Fp>","\u003Cp>Through molecular mimicry. The sugar coating on \u003Cem>Campylobacter\u003C\u002Fem> resembles molecules on human peripheral nerves. Antibodies made against the bacterium cross-react with the nerves and attack them, causing the ascending weakness of Guillain-Barré syndrome, usually a week or two after the diarrhea.\u003C\u002Fp>",{"question":258,"answer":259},"\u003Cp>Is Campylobacter oxidase positive or negative?\u003C\u002Fp>","\u003Cp>Oxidase-positive. This helps separate it from the Enterobacteriaceae, which are oxidase-negative. It is also catalase-positive.\u003C\u002Fp>",{"question":261,"answer":262},"\u003Cp>How do you tell Campylobacter from Vibrio?\u003C\u002Fp>","\u003Cp>Both are curved, oxidase-positive Gram-negative rods. \u003Cem>Campylobacter\u003C\u002Fem> is microaerophilic and grows at 42°C; \u003Cem>Vibrio\u003C\u002Fem> is a facultative anaerobe that grows on ordinary media and on TCBS agar.\u003C\u002Fp>",{"question":264,"answer":265},"\u003Cp>How is Campylobacter infection treated?\u003C\u002Fp>","\u003Cp>Most cases are self-limited and need only rehydration. When antibiotics are needed, a macrolide such as azithromycin is preferred. Fluoroquinolones like ciprofloxacin are now often unreliable because resistance is common.\u003C\u002Fp>",{"question":267,"answer":268},"\u003Cp>What is the difference between Campylobacter jejuni and Campylobacter fetus?\u003C\u002Fp>","\u003Cp>\u003Cem>C. jejuni\u003C\u002Fem> causes gut infection, grows at 42°C, and is sensitive to nalidixic acid. \u003Cem>C. fetus\u003C\u002Fem> causes bloodstream infection in the elderly and debilitated, grows at 25°C (not 42°C), and is resistant to nalidixic acid.\u003C\u002Fp>",[270],"gram-negative-rods",{"slug":272,"title":273,"description":274,"seoTitle":49,"seoDescription":49,"author":44,"createdDate":275,"lastUpdatedDate":276,"draft":47,"category":153,"image":49,"faq":277,"tags":299},"eosin-methylene-blue-emb-agar-composition-uses-colony-characteristics","EMB Agar: Composition, Principle, and Colony Morphology","\u003Cp>How eosin and methylene blue produce the metallic green sheen, why \u003Cem>Klebsiella \u003C\u002Fem>ferments lactose without one, how to read EMB plates in reflected versus transmitted light, and when EMB beats MacConkey.\u003C\u002Fp>","2013-08-23","2026-08-22",[278,281,284,287,290,293,296],{"question":279,"answer":280},"\u003Cp>Why does \u003Cem>E. coli\u003C\u002Fem> produce a metallic green sheen on EMB agar?\u003C\u002Fp>","\u003Cp>On the Levine EMB formulation used in most laboratories today, \u003Cem>E. coli\u003C\u002Fem> vigorously ferments lactose (the only sugar present), producing enough acid to sharply lower the pH at the colony surface. At this low pH, eosin Y and methylene blue precipitate in large quantities onto the colony. The densely packed dye crystals produce an iridescent metallic sheen, similar to a soap bubble, visible as green under reflected light. It is a direct indicator of vigorous acid production from lactose fermentation.\u003C\u002Fp>",{"question":282,"answer":283},"What is the difference between EMB and MacConkey agar?","\u003Cp>EMB (Levine): eosin Y + methylene blue dyes, contains lactose only, \u003Cem>E. coli\u003C\u002Fem> shows metallic green sheen. The original Holt-Harris-Teague EMB also contained sucrose, but Levine EMB is standard today. MacConkey: crystal violet + bile salts, contains lactose only, E. coli shows dark pink with bile precipitate halo.\u003C\u002Fp>",{"question":285,"answer":286},"\u003Cp>Why does \u003Cem>Klebsiella\u003C\u002Fem> produce mucoid colonies on EMB agar?\u003C\u002Fp>","\u003Cp>\u003Cem>Klebsiella\u003C\u002Fem> produces a thick polysaccharide capsule, using some fermented carbohydrate for capsule synthesis rather than acid production. Results in large, moist, dome-shaped mucoid colonies. On EMB they appear dark pink-brown and mucoid but without the metallic green sheen characteristic of \u003Cem>E. coli.\u003C\u002Fem>\u003C\u002Fp>",{"question":288,"answer":289},"Can gram-positive bacteria grow on EMB agar?","\u003Cp>No, eosin Y and methylene blue dyes are toxic to gram-positive organisms, penetrating gram-positive cell walls and disrupting membrane function. Most \u003Cem>Staphylococcus, Streptococcus\u003C\u002Fem>, and \u003Cem>Enterococcus\u003C\u002Fem> species are completely inhibited. EMB is not suitable when gram-positive pathogens are suspected.\u003C\u002Fp>",{"question":291,"answer":292},"What is the significance of EMB agar in water quality testing?","\u003Cp>EMB is FDA-BAM approved for \u003Cem>E. coli\u003C\u002Fem> detection in food and water. The metallic green sheen provides rapid, reliable presumptive fecal coliform identification. In the membrane filter technique, a measured water volume is filtered and the membrane placed on EMB, apperance of metallic green sheen colonies at 24–48 hours are counted as presumptive fecal coliforms.\u003C\u002Fp>",{"question":294,"answer":295},"\u003Cp>Why are \u003Cem>Salmonella\u003C\u002Fem> and \u003Cem>Shigella\u003C\u002Fem> colorless on EMB agar?\u003C\u002Fp>","\u003Cp>Both are non-lactose fermenters. Without acid production, the pH does not fall and dyes remain soluble rather than precipitating onto colonies. Colorless colonies on EMB suggest non-lactose fermenters but cannot distinguish \u003Cem>Salmonella\u002FShigella \u003C\u002Fem>from \u003Cem>Proteus\u003C\u002Fem> or \u003Cem>Pseudomonas, \u003C\u002Fem>for which TSI and specific antisera required.\u003C\u002Fp>",{"question":297,"answer":298},"What does a dark pink colony without metallic sheen indicate on EMB?","\u003Cp>Moderate lactose or sucrose fermentation, enough acid for dye precipitation but not enough for metallic sheen. Most typically \u003Cem>Klebsiella pneumoniae\u003C\u002Fem> (large, mucoid, dark pink-brown) and \u003Cem>Enterobacter\u003C\u002Fem> species. \u003Cem>E. coli\u003C\u002Fem> (metallic sheen) vs \u003Cem>Klebsiella \u003C\u002Fem>(dark, no sheen) is one of the most useful differential observations on EMB.\u003C\u002Fp>",[300],"bacterial-culture-media",{"enabled":302,"threads":303,"total":304},true,[],0,[306,312,319,326,332,337,343,348,354,357,364],{"slug":307,"name":44,"description":308,"image":309,"body":310,"postCount":311},"acharya-tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",481,{"slug":313,"name":314,"description":315,"image":316,"body":317,"postCount":318},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",79,{"slug":320,"name":321,"description":322,"image":323,"body":324,"postCount":325},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fsushmita-baniya-1.png","Sushmita Baniya holds an M.Sc. in Medical Microbiology from Tribhuvan University (National College), with a research focus in Genetics and Molecular Biology. She is actively involved in teaching and research in the field of microbiology.",26,{"slug":327,"name":328,"description":322,"image":329,"body":330,"postCount":331},"samikshya-acharya","Samikshya Acharya","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fsamikshya-acharya.jpeg","Samikshya Sharma completed her postgraduate studies in Medical Microbiology at the Central Department of Microbiology, Tribhuvan University, Nepal. She contributes to Microbeonline with the goal of making foundational and clinical microbiology concepts clear and useful for students in medical, laboratory science, and allied health programs.",20,{"slug":333,"name":334,"description":322,"image":49,"body":335,"postCount":336},"alisha-tripathi","Alisha Tripathi","Alisha Tripathi holds an M.Sc. in Medical Microbiology from National College, Tribhuvan University. With over a year of teaching experience, her academic interests span Molecular Biology, Immunology, and Genetics.",6,{"slug":338,"name":339,"description":340,"image":49,"body":341,"postCount":342},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor","Aastha Shrestha is a Biotechnology graduate with an M.Sc. from National College, Tribhuvan University. Her academic interests center on Molecular Biology and Immunology; two fields that are increasingly converging in modern diagnostic and clinical microbiology. \n\nShe contributes to Microbeonline with the goal of making complex concepts in these areas approachable and exam-relevant for students across medical, biotechnology, and laboratory science programs.",9,{"slug":344,"name":345,"description":346,"image":49,"body":49,"postCount":347},"guest-author","Guest Author","Guest Author \u002F Contributor",1,{"slug":349,"name":350,"description":322,"image":351,"body":352,"postCount":353},"srijana-khanal","Srijana Khanal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fsrijana-khanal-1.png","Srijana Khanal is a microbiology educator with nearly a decade of teaching experience, including her role as faculty in the Microbiology Department at National College, NIST. \n\nHer time in the classroom has given her a clear sense of where students struggle and what explanations actually work, a perspective that directly shapes how she writes.\n\nHer academic interests span Immunology, Genetics, Basic Sciences, and Research Methodology, and she brings the same rigor to her writing that she brought to teaching. Alongside academic writing, she has a passion for creative writing -- an instinct that shows in her ability to make dense scientific material readable without sacrificing accuracy.\n\nShe contributes to Microbeonline to extend her teaching reach beyond the classroom, helping medical and laboratory science students across the region build a stronger foundation in microbiology.",15,{"slug":355,"name":356,"description":346,"image":49,"body":49,"postCount":347},"dr-poonam-acharya","Dr. Poonam Acharya",{"slug":358,"name":359,"description":360,"image":361,"body":362,"postCount":363},"nisha-rijal","Nisha Rijal","Microbiologist and AMR Specialist Kathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fnisha-rijal-1.png","Nisha Rijal is a microbiologist with nearly 15 years of frontline diagnostic and surveillance experience at the National Public Health Laboratory (NPHL), national reference laboratory under the Department of Health Services, Nepal. She currently works as an AMR Support Officer at the World Health Organization (WHO), Nepal, where her work focuses on strengthening antimicrobial resistance surveillance systems and translating AMR data into actionable public health response.\n\nHer research, published in peer-reviewed journals and cited over 220 times, spans some of the most clinically significant infectious disease challenges in Nepal and South Asia: antimicrobial resistance trends in *Vibrio cholerae* across an 11-year national surveillance dataset, sero-epidemiology of scrub typhus in patients with acute febrile illness, lower respiratory tract infections in HIV-positive patients, and gonococcal resistance surveillance. She was a contributor to Nepal's National Antimicrobial Resistance Containment Action Plan, a foundational policy document for AMR governance in Nepal. You can find list of [Nisha Rijal's article here in Google Scholar.](https:\u002F\u002Fscholar.google.com\u002Fcitations?user=N-Ruq54AAAAJ&hl=en)\n\nThis depth of experience is visible in her writing at Microbeonline. Her 53 published articles cover bacteriology, parasitology, mycology, immunology, and laboratory techniques, and are consistently among the most detailed and clinically grounded content on the site. She brings to every article the same standard that national reference laboratory work demands: methodological precision, awareness of real diagnostic constraints, and an understanding of what results actually mean for patient care in resource-limited settings.\n\nHer areas of particular expertise include antimicrobial susceptibility testing and resistance mechanism detection, quality assurance in clinical microbiology, and laboratory-based infectious disease surveillance.\n\n---\n\n*Nisha Rijal contributes to Microbeonline in a personal capacity. Her views and writing do not represent the positions of the World Health Organization or any other institution.*",54,{"slug":365,"name":366,"description":367,"image":368,"body":369,"postCount":347},"padma-shrestha","Padma Shrestha","Author","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fpadma-shrestha.png","Padma Shrestha is from Kathmandu, Nepal. She has completed Masters degree in Medical microbiology from Tribhuvan University. She has great interest in Microbiology and Molecular Biology.",[371,377,383,388,392,397,401,405,409,414,418,423,428,433,438,442,446,450,455,460,464,468,472,477,481,485,489,493,498,503,507,511,515,519,523,527,531,535,539,543,547,551,555,559,563,567,571,575,580,584,588,592,596,600,603,606,610,614,618,622,626,630,634,638,642,646,650,654,657,661,664,667,670,673,676,679,682,685,687,690,693,696],{"slug":237,"name":372,"description":373,"image":374,"body":375,"postCount":376},"Gram-Negative Cocci and Coccobacilli","Neisseria, Moraxella, Haemophilus and related gram-negative coccal organisms","https:\u002F\u002Fassets.microbeonline.com\u002Ftags\u002Fgram-negative-cocci.png","# Gram Negative Cocci\n\nNeisseria gonorrhoeae, Neisseria meningitides, Moraxella catarrhalis, and other Neisseria spp. are clinically relevant gram-negative cocci.\n\nN. gonorrhoeae is the leading cause of sexually transmitted disease whereas N. meningitides is a leading cause of fatal bacterial meningitis.",14,{"slug":378,"name":379,"description":380,"image":49,"body":381,"postCount":382},"microscopy","Microscopy","Microscope types, components, and microscopy techniques","These are list of blog posts related to microscopy. ",12,{"slug":384,"name":385,"description":386,"image":49,"body":49,"postCount":387},"gram-positive-cocci","Gram-Positive Cocci","Staphylococcus, Streptococcus, Enterococcus, Micrococcus — organisms, diseases, and identification tests",11,{"slug":270,"name":389,"description":390,"image":49,"body":49,"postCount":391},"Gram-Negative Rods (Other than Enterobacteriaceae)","\u003Cp>Gram negative rods other than members of Enterobacteriaceae family such as  Pseudomonas, Acinetobacter and related organisms\u003C\u002Fp>",5,{"slug":393,"name":394,"description":395,"image":49,"body":49,"postCount":396},"gram-positive-rods","Gram-Positive Rods","Bacillus, Clostridium, Listeria, Corynebacterium, Actinomyces and related organisms",8,{"slug":398,"name":399,"description":400,"image":49,"body":49,"postCount":387},"mycobacteria","Mycobacteria","Mycobacterium tuberculosis, leprosy, atypical mycobacteria, and acid-fast organism diagnosis",{"slug":402,"name":403,"description":404,"image":49,"body":49,"postCount":387},"anaerobic-bacteriology","Anaerobic Bacteriology","Anaerobic organisms, anaerobic culture methods, and anaerobic infection diagnosis",{"slug":406,"name":407,"description":408,"image":49,"body":49,"postCount":382},"enterobacteriaceae","Enterobacteriaceae","Identification, differentiation, and clinical significance of Enterobacteriaceae family members",{"slug":410,"name":411,"description":412,"image":49,"body":49,"postCount":413},"spirochetes","Spirochetes","Treponema, Leptospira, Borrelia and spirochetal infections",7,{"slug":415,"name":416,"description":417,"image":49,"body":49,"postCount":376},"food-microbiology","Food Microbiology","Food-borne pathogens, food safety, spoilage, and preservation",{"slug":419,"name":420,"description":421,"image":49,"body":49,"postCount":422},"antimicrobial-susceptibility-testing","Antimicrobial Susceptibility Testing","Methods for testing antibiotic susceptibility in clinical microbiology",21,{"slug":424,"name":425,"description":426,"image":49,"body":49,"postCount":427},"antimicrobials-moa-amr","Antimicrobials (MOA & AMR)","Mechanisms, detection, and clinical significance of antimicrobial resistance",13,{"slug":429,"name":430,"description":431,"image":49,"body":49,"postCount":432},"sterilization-disinfection","Sterilization and Disinfection","Methods of sterilization and disinfection in healthcare and laboratory settings",10,{"slug":434,"name":435,"description":436,"image":49,"body":49,"postCount":437},"specimen-collection-transport","Specimen Collection and Transport","Collection, handling, and transport of clinical specimens for microbiological testing",27,{"slug":439,"name":440,"description":441,"image":49,"body":49,"postCount":422},"bacterial-structure-physiology","Bacterial Structure and Physiology","Bacterial cell structure, growth, physiology, and environmental factors affecting growth",{"slug":443,"name":444,"description":49,"image":49,"body":445,"postCount":336},"horizontal-gene-transfer","Horizontal Gene Transfer","Articles related to **Horizontal Gene Transfer**",{"slug":447,"name":448,"description":49,"image":49,"body":449,"postCount":432},"chromatography","Chromatography","Information about chromatographic techniques.",{"slug":451,"name":452,"description":453,"image":49,"body":454,"postCount":413},"electrophoresis","Electrophoresis","Information about Electrophoresis Techniques ","Detailed information  about Electrophoresis Techniques ",{"slug":456,"name":457,"description":458,"image":49,"body":459,"postCount":336},"pcr-techniques","PCR Techniques","Information about various types of Polymerase Chain Reaction Techniques ","More detailed information about various types of Polymerase Chain Reaction Techniques ",{"slug":461,"name":462,"description":463,"image":49,"body":49,"postCount":336},"bacteriophage","Bacteriophage","Description about Bacteriophage.",{"slug":465,"name":466,"description":467,"image":49,"body":49,"postCount":336},"malaria","Malaria","It is the collections of articles regarding malarial disease. ",{"slug":469,"name":470,"description":471,"image":49,"body":49,"postCount":336},"anaerobic-culture-techniques","Anaerobic Culture Techniques","Posts related with Anaerobic Culture Techniques.",{"slug":473,"name":474,"description":475,"image":49,"body":49,"postCount":476},"immunoassays","Immunoassays","You will get information about all the diagnostic tests that rely on the specific binding between an antigen and an antibody to detect or quantify a substance.",19,{"slug":478,"name":479,"description":480,"image":49,"body":49,"postCount":413},"biosafety-levels","Biosafety levels ","Articles related to Biosafety Levels",{"slug":482,"name":483,"description":484,"image":49,"body":49,"postCount":391},"environmental-factors","Environmental Factors ","In this case we are talking about growth requirements of microorganisms with deep dive in environmental factors that affect the growth. ",{"slug":486,"name":487,"description":488,"image":49,"body":49,"postCount":336},"pipette","Pipette","Posts related with Pipette. ",{"slug":490,"name":491,"description":492,"image":49,"body":49,"postCount":396},"bacteriology-mcqs","Bacteriology MCQs","This sections lists MCQs in Bacteriology.",{"slug":494,"name":495,"description":496,"image":49,"body":49,"postCount":497},"parasitology-mcqs","Parasitology MCQs","This section lists MCQs in Parasitology.",2,{"slug":499,"name":500,"description":501,"image":49,"body":49,"postCount":502},"virology-mcqs","Virology MCQs","This is the collections of Multiple Choice Questions in Virology.",4,{"slug":504,"name":505,"description":506,"image":49,"body":49,"postCount":391},"mcqs-in-microbiology","MCQs in Microbiology","This section lists the collections of Multiple Choice Questions in General Microbiology Topics. ",{"slug":508,"name":509,"description":510,"image":49,"body":49,"postCount":396},"immunology-mcqs","Immunology MCQs","In this section; we are posting collections of Multiple Choice Questions about Immunology. ",{"slug":512,"name":513,"description":514,"image":49,"body":49,"postCount":342},"microbial-curiosities","Microbial Curiosities","In this clusters, we are posting interesting and unique information about Microorganisms. ",{"slug":300,"name":516,"description":517,"image":49,"body":49,"postCount":518},"Bacterial Culture Media","Posts related to Bacterial Culture Media. ",23,{"slug":520,"name":521,"description":522,"image":49,"body":49,"postCount":336},"fungal-culture-media","Fungal Culture Media","Posts related to Fungal Culture Media.",{"slug":524,"name":525,"description":526,"image":49,"body":49,"postCount":391},"motility-test","Motility Test","This lists the procedure regarding various tests methods for bacterial motility.",{"slug":528,"name":529,"description":530,"image":49,"body":49,"postCount":432},"bacterial-enumeration","Bacterial enumeration","These posts are related to isolation and enumeration of bacteria. ",{"slug":532,"name":533,"description":534,"image":49,"body":49,"postCount":497},"gram-positive-coccobacillus","Gram-positive coccobacillus","List of Gram Positive Coccobacilli",{"slug":536,"name":537,"description":538,"image":49,"body":49,"postCount":502},"dimorphic-fungi","Dimorphic Fungi","This is about various dimorphic fungi. ",{"slug":540,"name":541,"description":542,"image":49,"body":49,"postCount":413},"bacterial-classification","Bacterial Classification","These posts are related with various approaches used for the classification of Bacteria. ",{"slug":544,"name":545,"description":546,"image":49,"body":49,"postCount":391},"immunofluorescence","Immunofluorescence ","Various Tests related to Immunofluorescence ",{"slug":548,"name":549,"description":550,"image":49,"body":49,"postCount":342},"antibody-mediated-immunity","Antibody-mediated Immunity","This clusters links the articles that are sharing insights about Antibody-mediated immunity. ",{"slug":552,"name":553,"description":554,"image":49,"body":49,"postCount":413},"hypersensitivity","Hypersensitivity","Articles related to Hypersensitivity.",{"slug":556,"name":557,"description":49,"image":49,"body":49,"postCount":558},"haemophilus","Haemophilus",3,{"slug":560,"name":561,"description":562,"image":49,"body":49,"postCount":502},"sexually-transmitted-infections-stis","Sexually transmitted infections (STIs)","This is the clusters of infections that are transmitted sexually. ",{"slug":564,"name":565,"description":566,"image":49,"body":49,"postCount":382},"adaptive-immunity","Adaptive Immunity","Blog posts related to B Cell Immunity and T Cell Immunity.",{"slug":568,"name":569,"description":570,"image":49,"body":49,"postCount":376},"fungal-diagnostics","Fungal Diagnostics","Various methods used for the Diagnosis of Fungal Infections. ",{"slug":572,"name":573,"description":574,"image":49,"body":49,"postCount":391},"laboratory-storage-and-preservation","Laboratory Storage and Preservation","Articles about Laboratory Storage of Antimicrobial Disk, Test organisms and Equipment used for this process. ",{"slug":576,"name":577,"description":578,"image":49,"body":579,"postCount":336},"laboratory-heating-equipment","Laboratory Heating Equipment","A guide to laboratory heating equipment, including hot plates, water baths, Bunsen burners, incubators, and dry baths, and how to choose the right one for each task.","Laboratory heating equipment covers the instruments that warm, melt, incubate, or sterilize samples and media in a microbiology laboratory. Each one delivers heat differently. \n\nA hot plate gives high, direct, dry heat; a water bath gives gentle, even, wet heat up to about 100°C; a Bunsen burner gives an open flame for rapid, very high heat; an incubator holds cultures at a steady temperature over hours or days; and a dry bath heats small tubes without water. Choosing the right one depends on the temperature you need, how precise it must be, and whether the sample can tolerate direct or open-flame heat.\n\nThe articles below cover each piece of heating equipment in detail, including its parts, working principle, uses, and the mistakes that most often go wrong at the bench.",{"slug":581,"name":582,"description":583,"image":49,"body":49,"postCount":342},"laboratory-glassware","Laboratory Glassware","Posts about Laboratory Glassware. ",{"slug":585,"name":586,"description":587,"image":49,"body":49,"postCount":336},"helminths","Helminths","In this section, we are covering properties, life cycle, pathogenesis and laboratory diagnosis of Helminths\u002FHelminthic infestations. ",{"slug":589,"name":590,"description":591,"image":49,"body":49,"postCount":413},"protozoan-parasite","Protozoan Parasite","In this cluster, we are covering protozoan parasites. ",{"slug":593,"name":594,"description":595,"image":49,"body":49,"postCount":347},"tests-for-gram-positive-cocci","Biochemical Tests for Gram Positive Cocci","This is the lists of Biochemical Tests that are used for Gram Positive Cocci. ",{"slug":597,"name":598,"description":599,"image":49,"body":49,"postCount":432},"bacterial-staining-technique","Bacterial Staining Technique","Lists of various staining techniques that are used to stain bacteria. ",{"slug":77,"name":601,"description":602,"image":49,"body":49,"postCount":422},"Enzyme Tests","\u003Cp>Various Biochemical Test that are based on enzymatic activity of the microorganisms. \u003C\u002Fp>",{"slug":111,"name":604,"description":605,"image":49,"body":49,"postCount":387},"Carbohydrate Utilization","\u003Cp>Various biochemical tests which are related to Carbohydrate fermentation or Utilization\u003C\u002Fp>",{"slug":607,"name":608,"description":609,"image":49,"body":49,"postCount":391},"susceptibility-based-id","Susceptibility-based ID","\u003Cp>These are susceptibility based identification test such as optochin sensitivity, bacitracin sensitivity etc. \u003C\u002Fp>",{"slug":611,"name":612,"description":613,"image":49,"body":49,"postCount":502},"microbial-metabolism","Microbial Metabolism","\u003Cp>Tests about Microbial Metabolism. \u003C\u002Fp>",{"slug":615,"name":616,"description":617,"image":49,"body":49,"postCount":396},"substrate-utilization","Substrate Utilization","\u003Cp>The test in which a non-sugar carbon\u002Fnitrogen source is used or degraded (citrate, malonate, decarboxylases, indole, PAD).\u003C\u002Fp>",{"slug":619,"name":620,"description":621,"image":49,"body":49,"postCount":558},"atypical-pneumonia","Atypical Pneumonia","\u003Cp>Organisms responsible for Atypical Pneumonia. \u003C\u002Fp>",{"slug":623,"name":624,"description":625,"image":49,"body":49,"postCount":391},"antigen","Antigen","\u003Cp>Various articles related to Antigens.\u003C\u002Fp>",{"slug":627,"name":628,"description":629,"image":49,"body":49,"postCount":413},"innate-immunity","Innate Immunity","\u003Cp>Articles related to Innate Immunity. \u003C\u002Fp>",{"slug":631,"name":632,"description":633,"image":49,"body":49,"postCount":502},"respiratory-tract-infection","Respiratory Tract Infection","\u003Cp>In this cluster, you can see various etiological agents that causes respiratory tract infection. \u003C\u002Fp>",{"slug":635,"name":636,"description":637,"image":49,"body":49,"postCount":391},"torch-infection","TORCH Infection","\u003Cp>In this section; you can find articles related with TOCH infection. \u003C\u002Fp>",{"slug":639,"name":640,"description":641,"image":49,"body":49,"postCount":413},"microbiology-for-beginners","Microbiology for Beginners","\u003Cp>These articles are very basic articles, which will share general concepts in Microbiology. \u003C\u002Fp>",{"slug":643,"name":644,"description":645,"image":49,"body":49,"postCount":336},"dna-replication","DNA Replication","\u003Cp>Articles related to DNA and Replication of DNA. \u003C\u002Fp>",{"slug":647,"name":648,"description":649,"image":49,"body":49,"postCount":413},"genetic-code","Genetic Code","\u003Cp>Articles related to Genetic Code.\u003C\u002Fp>",{"slug":651,"name":652,"description":653,"image":49,"body":49,"postCount":413},"molecular-technique","Molecular Technique","\u003Cp>Posts related to Molecular Techniques. \u003C\u002Fp>",{"slug":655,"name":656,"description":49,"image":49,"body":49,"postCount":347},"colorimetric-assay","Colorimetric Assay ",{"slug":658,"name":659,"description":660,"image":49,"body":49,"postCount":391},"pharmaceutical-microbiology","Pharmaceutical Microbiology","\u003Cp>Various articles related to Pharmaceutical Microbiology\u003C\u002Fp>",{"slug":662,"name":663,"description":49,"image":49,"body":49,"postCount":558},"blood-and-immune-cells","Blood and Immune Cells",{"slug":665,"name":666,"description":49,"image":49,"body":49,"postCount":391},"host-pathogen-interaction","Host Pathogen Interaction",{"slug":668,"name":669,"description":49,"image":49,"body":49,"postCount":502},"blood-culture","Blood Culture",{"slug":671,"name":672,"description":49,"image":49,"body":49,"postCount":502},"environmental-microbiology","Environmental microbiology ",{"slug":674,"name":675,"description":49,"image":49,"body":49,"postCount":336},"copromicroscopic-technique","Copromicroscopic Technique",{"slug":677,"name":678,"description":49,"image":49,"body":49,"postCount":558},"quality-control","Quality Control",{"slug":680,"name":681,"description":49,"image":49,"body":49,"postCount":502},"dermatophytes","Dermatophytes",{"slug":683,"name":684,"description":49,"image":49,"body":49,"postCount":558},"viral-hemorrhagic-fevers","Viral Hemorrhagic Fevers",{"slug":112,"name":686,"description":49,"image":49,"body":49,"postCount":502},"H2S Production",{"slug":688,"name":689,"description":49,"image":49,"body":49,"postCount":497},"water-quality-testing","Water Quality Testing",{"slug":691,"name":692,"description":49,"image":49,"body":49,"postCount":391},"virology-basics","Virology basics",{"slug":694,"name":695,"description":49,"image":49,"body":49,"postCount":502},"typing-methods","Typing Methods",{"slug":697,"name":698,"description":49,"image":49,"body":49,"postCount":558},"blotting-technique","Blotting Technique"]