[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fi-U4K4X2U58prvIL4yuxco4n4O7V6KpKH0ULK1yBLMU":36,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":303,"$fucxFBm2ZjZfGSdmdRaSNGBI_F0jJme4f0GTvzUhQfL8":367},[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":42,"author":43,"createdDate":44,"lastUpdatedDate":45,"draft":46,"category":47,"image":42,"body":48,"faq":49,"commentsClosed":46,"tags":71,"related":73,"comments":299},"onpg-test-galactosidase-principle-procedure-results","ONPG Test: How to Catch the Lactose Fermenters That the Lactose Test Misses","Some organisms have the enzyme to ferment lactose but lack the transporter to get lactose into the cell, so a standard lactose test calls them non-fermenters. ONPG is a lactose look-alike that slips into the cell without the transporter and tests the enzyme directly. Here is the two-protein logic, why the toluene step matters, and how ONPG rescues the late and cryptic lactose fermenters.",null,"Acharya Tankeshwar","2015-02-06","2026-08-24",false,"biochemical-tests","The organism that could ferment lactose but got filed as one that couldn't\n\nA Gram-negative rod from a stool sample is streaked onto MacConkey agar. After overnight incubation the colonies are pale. Non-lactose fermenter, the technician notes, which in a stool workup pushes the organism toward the *Salmonella* and *Shigella* end of the bench, the pathogens worth chasing.\n\nBut this organism is not a non-fermenter. It carries a perfectly good β-galactosidase, the enzyme that splits lactose. What it lacks is an efficient **permease**, the membrane transporter that carries lactose into the cell in the first place. The enzyme is inside, waiting, with no substrate reaching it. On MacConkey, which reads acid produced from lactose, the organism looks negative because the lactose never got in to be fermented.\n\nThis is a **late** or **cryptic** lactose fermenter, and if you stop at the MacConkey plate you will misclassify it.\n\nThe ONPG test exists precisely to catch this organism. ONPG is a synthetic molecule built to look like lactose to the enzyme, but small and permeable enough to slip into the cell **without needing the permease.** Once inside, β-galactosidase cleaves it and releases a bright yellow compound. The organism that looked negative on lactose turns the ONPG tube yellow, revealing the enzyme that was there all along.\n\nOne test reads the transporter and the enzyme together. The other reads the enzyme alone. Knowing the difference is what keeps a late lactose fermenter from being mistaken for a pathogen it is not. This article is about that difference.\n\n## Principle of ONPG Test\n\nO-Nitrophenyl-β-D-galactopyranoside (ONPG) is structurally similar to lactose (i.e. O-Nitrophenyl-β-D-galactopyranoside is an analog of lactose), except that orthonitrophenyl has been substituted for glucose.\n\nOn hydrolysis, through the action of the enzyme β-galactosidase, ONPG cleaves into two residues, galactose and o-nitrophenol. ONPG itself is colorless; the o-nitrophenol released when it is cleaved is yellow, and that yellow is the visual evidence of hydrolysis.\n\n![ONPG Test - ONPG Test](\u002Fblogs\u002FONPG-Structure.png)Figure: ONPG Test\n\nLactose fermenting bacteria possess both lactose permease and β-galactosidase, two enzymes required for the production of acid in the lactose fermentation test. The permease is required for the lactose molecule to penetrate the bacterial cell where the β-galactosidase can cleave the galactoside bond, producing glucose and galactose.\n\nNon-lactose fermenting bacteria are devoid of both enzymes and are incapable of producing acid from lactose.\n\nSome bacterial species appear to be non-lactose fermenters because they **lack permease, but do possess β-galactosidase and give a positive ONPG test**. So-called late lactose fermenters may be delayed in their production of acid from lactose because of sluggish permease activity. In these instances, a positive test may provide rapid identification of delayed lactose fermentation.\n\n### Why lactose fermentation needs two proteins, and ONPG needs only one\n\nFermenting lactose is a two-step problem, and each step has its own protein.\n\n**Step one: get lactose into the cell.** Lactose is a disaccharide and cannot cross the bacterial membrane on its own. It needs a dedicated transporter, **lactose permease**, to carry it inside.\n\n**Step two: split it once inside.** Within the cell, the enzyme **β-galactosidase** cleaves lactose into glucose and galactose, which the organism then ferments to acid.\n\nA standard lactose test, such as MacConkey agar or the lactose reaction in TSI, detects the acid produced at the end of step two. To make that acid, the organism needs *both* proteins: the permease to admit the lactose and the enzyme to split it. Miss either one and the test reads negative.\n\nThis creates a blind spot. An organism that has β-galactosidase but lacks the permease, or has a slow, sluggish permease, cannot get enough lactose inside to make detectable acid quickly. On MacConkey it looks like a non-fermenter or a slow, late fermenter. But it is not enzyme-deficient. It is transporter-deficient.\n\n**ONPG removes the transporter from the question.** ONPG (o-nitrophenyl-β-D-galactopyranoside) is a synthetic analog of lactose. To β-galactosidase it looks enough like lactose to be cleaved. But unlike lactose, ONPG is small and lipophilic enough to **diffuse into the cell without a permease.** It reaches the intracellular enzyme on its own.\n\nSo ONPG tests β-galactosidase in isolation, independent of whether the organism can transport lactose. If the enzyme is present, ONPG is cleaved and the tube turns yellow, whether or not the organism has a working permease.\n\nPut the two tests side by side and they answer different questions:\n\n|  | Lactose test (MacConkey, TSI) | ONPG test |\n| --- | --- | --- |\n| Needs permease? | Yes | No |\n| Needs β-galactosidase? | Yes | Yes |\n| Reads | Transporter **and** enzyme together | Enzyme alone |\n| Misses | Enzyme-positive, permease-poor organisms | Nothing on the transport side |\n\nThe reason ONPG is worth running is entirely in that bottom row. It rescues the organisms the lactose test wrongly files as negative.\n\n**Media and Reagents**\n\n1. Sodium phosphate buffer, 1 M, pH 7.0\n2. O-Nitrophenyl-β-D-galactopyranoside, 0.75 M\n3. Physiologic saline\n4. Toluene\n\n## Quality control\n\n1. Positive control: *Escherichia coli* ATCC 25922, yellow (β-galactosidase present)\n2. Negative control: *Proteus vulgaris* ATCC 13315, colorless (no β-galactosidase)\n\nRun controls with each new lot of ONPG substrate or tablets, since the substrate degrades and can give false negatives if old.\n\n## Procedure\n\nBacteria grown in a medium containing lactose (to induce the production of the galactosidase enzyme), such as [Kligler iron agar (KIA)](\u002Fkliglers-iron-agar-kia-principle-procedure-and-results\u002F) or Triple Sugar Iron (TSI) agar, produces optimal results in this test.\n\n**Note:** β-galactosidase  enzyme (inducible enzyme)  is made ONLY in the presence of the lactose substrate\n\n1. A loopful of bacterial growth is emulsified in 0.05mL of physiologic saline to produce a heavy suspension\n2. One drop of toluene is added to the suspension and vigorously mixed for a few seconds to release the enzyme from bacterial cells.\n3. An equal quantity of buffered ONPG solution is added to the suspension.\n4. The mixture is placed in a 37°C water bath\n\n**When Using ONPG Tablets**\n\n1. A loopful of bacterial suspension is added directly to the ONPG substrate resulting from adding 1mL of distilled water to a tablet in a test tube.\n2. This suspension is also placed in a 37°C water bath\n\n**Why toluene?** \\\nToluene is a solvent that permeabilizes the bacterial membrane, releasing β-galactosidase from inside the cell so it can act on the ONPG in solution directly. ONPG can diffuse into an intact cell on its own, but permeabilizing the cell speeds the reaction by removing even that small barrier and letting a large amount of enzyme meet the substrate at once. It makes a slow reaction fast, which is why the conventional method reads within minutes to an hour. The tablet method skips the toluene step and relies on ONPG's own ability to enter intact cells, which is why it can be slower.\n\n## Results and Interpretations\n\nThe rate of hydrolysis of ONPG to o-nitrophenol may be rapid for some organisms; producing a visible yellow color reaction within 5 to 10 minutes.\n\n![ONPG Test results - ONPG Test results](\u002Fblogs\u002FONPG-test-results-300x270.png)Figure: ONPG Test results\n\nMost tests are positive within 1 hour; however, reactions should not be interpreted as negative before 24 hours of incubation.\n\nThe yellow color is usually distinct and indicates that the organism has produced o-nitrophenol from the ONPG substrate through the action of β-galactosidase.\n\n## ONPG test results vs. lactose fermentation\n\n1. **Lactose fermenter (ONPG Positive)**: *E. coli, Klebsiella spp, Enterobacter spp* **produce β-galactosidase and permease**\n\n2. **Late lactose fermenter (ONPG Positive)**: *Citrobacter spp, Arizona spp* **produce only β-galactosidase** so they slowly ferment lactose.\n\n3. **Non-lactose fermenter (ONPG Negative):** most *Salmonella* serotypes, *Shigella* species (except some *S. sonnei*), *Proteus*, *Providencia*, and *Morganella* lack β-galactosidase and cannot ferment lactose by any route.\n\n   **A useful exception:** *Salmonella enterica* subsp. *arizonae* (the old \"*Arizona*\") is ONPG positive and a late lactose fermenter, unlike the common *Salmonella* serotypes. And *Shigella sonnei* is often ONPG positive despite being a non-lactose fermenter on MacConkey, a classic demonstration of the enzyme-present, permease-poor pattern. These exceptions are exactly the organisms ONPG was designed to reveal.\n\n## How to remember\n\n**Two locks, one key that skips a lock.**\n\nLactose fermentation has two locks: the permease lock (getting in) and the enzyme lock (getting split). A standard lactose test needs both locks opened. ONPG is a skeleton key that ignores the permease lock entirely, walks into the cell on its own, and tests only the enzyme lock. So when the lactose test says no but ONPG says yes, you have found an organism whose permease lock was stuck, not one that lacks the enzyme.\n\n**ONPG rescues the \"shy\" fermenters.**\n\nPicture a late lactose fermenter as an organism that *can* do the job but is slow to let the substrate in. MacConkey gives up on it too early and calls it negative. ONPG is patient in a different way: it hands the enzyme its substrate directly, so the shy fermenter finally shows its yellow. Ask yourself when you see a MacConkey-negative, ONPG-positive result: *is this really a non-fermenter, or just a slow one that got mislabeled?*\n\n**Yellow means the enzyme is home.**\n\nONPG is colorless; cleaving it releases yellow o-nitrophenol. Yellow tube equals β-galactosidase present, full stop, regardless of what the lactose plate said. The two exceptions worth naming, *Shigella sonnei* and *Salmonella* Arizonae, are precisely the organisms this test was built to catch.\n\n## Key exam facts\n\n| Question | Answer | The reason behind it |\n| --- | --- | --- |\n| What does ONPG detect? | β-galactosidase, in isolation | ONPG reaches the enzyme without needing a permease |\n| What is ONPG? | A synthetic analog of lactose (o-nitrophenyl-β-D-galactopyranoside) | Looks like lactose to the enzyme; small enough to enter without a transporter |\n| What does the enzyme release? | Galactose + o-nitrophenol (yellow) | The yellow is the readout |\n| Positive result | Yellow | β-galactosidase cleaved the ONPG |\n| Negative result | Colorless after 24 hours | No β-galactosidase |\n| Two proteins in lactose fermentation | Lactose permease (transport) + β-galactosidase (cleavage) | Both are needed to make acid from lactose |\n| Why does a lactose test miss some fermenters? | It needs both proteins; permease-poor organisms read negative | Not enough lactose gets in to make detectable acid |\n| Why does ONPG catch them? | It bypasses the permease and tests the enzyme directly | Transport is removed from the question |\n| What are late\u002Fcryptic fermenters? | Enzyme-positive, permease-poor organisms | Ferment lactose slowly or not visibly on MacConkey |\n| Classic late fermenters | *Citrobacter*, *Salmonella* Arizonae | β-galactosidase present, permease slow |\n| Classic cryptic exception | *Shigella sonnei* (often ONPG positive) | Non-fermenter on MacConkey but has the enzyme |\n| Why grow on lactose first? | β-galactosidase is inducible; lactose induces it | Growing on KIA\u002FTSI (lactose-containing) ensures the enzyme is expressed |\n| Why toluene? | Permeabilizes the cell to release enzyme and speed the reaction | Makes a slow reaction fast |\n| Reading window | Positive often within 1 hour; negative not before 24 hours | Some organisms hydrolyze slowly |\n| QC positive | *E. coli* ATCC 25922 (yellow) | Has β-galactosidase |\n| QC negative | *Proteus vulgaris* ATCC 13315 (colorless) | No β-galactosidase |\n| Main use | Identify late\u002Fcryptic lactose fermenters among Enterobacteriaceae | Resolves the transport blind spot of the lactose test |\n\n## Where students get confused\n\n**\"ONPG positive means the organism ferments lactose.\"** Not exactly. ONPG positive means the organism has β-galactosidase. Whether it ferments lactose in practice also depends on the permease. An organism can be ONPG positive and still read as a non-fermenter on MacConkey if its permease is absent or slow. That mismatch is not an error; it is the entire diagnostic point of the test.\n\n**Confusing what ONPG and the lactose test each measure.** The lactose test measures acid production, which needs the transporter and the enzyme together. ONPG measures the enzyme alone. When the two disagree, the organism has the enzyme but a transport problem. Reading them as interchangeable throws away the one piece of information ONPG uniquely provides.\n\n**Not understanding why toluene is added.** It looks contradictory: ONPG can enter an intact cell, so why break the cell open? Because permeabilizing the cell releases a large amount of enzyme to meet the substrate at once, turning a slow reaction into a fast one. Toluene is about speed, not about getting ONPG in.\n\n**Reading a negative too early.** Some organisms hydrolyze ONPG slowly. A tube that is colorless at one hour is not yet negative. The result should not be called negative before 24 hours of incubation.\n\n**Forgetting to induce the enzyme.** β-galactosidase is an inducible enzyme, made only when lactose is present. If the organism was grown on a medium without lactose, the enzyme may not be expressed and a true positive can read negative. Grow the organism on a lactose-containing medium such as KIA or TSI first.\n\n**Missing the *Shigella sonnei* and *Salmonella* Arizonae exceptions.** These are the organisms that look like non-fermenters but are ONPG positive, and they are exactly what the test was built to reveal. In a stool workup, remembering that some *Shigella sonnei* are ONPG positive prevents both confusion and misidentification.\n\n**Using degraded substrate.** ONPG substrate and tablets deteriorate over time and with light exposure. Old substrate gives false negatives. Run a positive control with each new lot.\n\n**References**\n\n1. Lowe GH. The rapid detection of lactose fermentation in paracolon organisms by the demonstration of β-D-galactosidase. *J Med Lab Technol.* 1962;19:21-25.\n2. Le Minor L, Ben Hamida F. Advantages of the ONPG test in *Salmonella* and *Arizona* identification. *Ann Inst Pasteur.*\n3. LaPage SP, Efstratiou A, Hill LR. The ortho-nitrophenol (ONPG) test and acid from lactose in Gram-negative genera. *J Clin Pathol.* 1973;26(11):821-825. doi:10.1136\u002Fjcp.26.11.821\n4. Buelow P. The ONPG test in diagnostic bacteriology: methodological investigations. *Acta Pathol Microbiol Scand.* 1964;60:376-386. doi:10.1111\u002Fapm.1964.60.3.376\n5. 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.\n6. Tille PM. *Bailey and Scott's Diagnostic Microbiology.* 15th ed. St. Louis: Elsevier; 2022.",[50,53,56,59,62,65,68],{"question":51,"answer":52},"What is the difference between the ONPG test and a lactose fermentation test?","A lactose test such as MacConkey or TSI measures acid produced from lactose, which requires two proteins working together: lactose permease to transport lactose into the cell, and beta-galactosidase to split it once inside. The ONPG test measures only the enzyme. ONPG is a synthetic lactose analog small enough to enter the cell without a permease, so it reaches beta-galactosidase directly. This means ONPG detects organisms that have the enzyme but lack an efficient transporter, which the lactose test would wrongly call non-fermenters.",{"question":54,"answer":55},"Why would an organism be ONPG positive but negative on MacConkey?","Because it has beta-galactosidase but lacks or is slow at lactose permease. Without an efficient transporter, not enough lactose gets into the cell to produce detectable acid on MacConkey, so the organism looks like a non-lactose fermenter. ONPG bypasses the transporter and reaches the enzyme directly, revealing that the enzyme was there all along. These are the late or cryptic lactose fermenters, and catching them is the whole purpose of the test.",{"question":57,"answer":58},"What does a positive ONPG test look like?","A yellow color. ONPG itself is colorless. When beta-galactosidase cleaves it, it releases o-nitrophenol, which is bright yellow. A yellow tube means the enzyme is present. A tube that stays colorless after 24 hours is negative.",{"question":60,"answer":61},"Why is toluene added in the ONPG test?","Toluene permeabilizes the bacterial membrane, releasing beta-galactosidase from inside the cells so it can act on the ONPG in solution directly. ONPG can diffuse into an intact cell on its own, but permeabilizing the cell lets a large amount of enzyme meet the substrate at once, turning a slow reaction into a fast one. Toluene is about speeding the reaction, not about getting ONPG into the cell. The tablet method omits toluene and relies on ONPG entering intact cells, which is why it can be slower.",{"question":63,"answer":64},"Why must the organism be grown on a lactose-containing medium before the ONPG test?","Because beta-galactosidase is an inducible enzyme, produced only when lactose is present. If the organism is grown without lactose, the enzyme may not be expressed, and a genuinely positive organism can read as negative. Growing it first on a lactose-containing medium such as Kligler iron agar or TSI induces the enzyme so the test can detect it.",{"question":66,"answer":67},"Which organisms are the classic ONPG exceptions?","Shigella sonnei is often ONPG positive despite appearing as a non-lactose fermenter on MacConkey, and Salmonella enterica subspecies arizonae is ONPG positive and a late lactose fermenter, unlike the common Salmonella serotypes which are ONPG negative. These enzyme-positive, transport-limited organisms are exactly what the ONPG test was designed to reveal.",{"question":69,"answer":70},"How long should I wait before calling an ONPG test negative?","A positive reaction often appears within an hour and sometimes within 5 to 10 minutes for rapid hydrolyzers. However, some organisms cleave ONPG slowly, so a colorless tube should not be recorded as negative before 24 hours of incubation. Reading a negative too early is a common error.",[72],"enzyme-tests",[74,84,107,141,173,205,236,267],{"slug":75,"title":76,"description":77,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":78,"lastUpdatedDate":79,"draft":46,"category":47,"image":42,"faq":80,"tags":81},"kliglers-iron-agar-kia-principle-procedure-and-results","Kligler’s Iron Agar (KIA): Principle, Procedure, Results","\u003Cp>A faint black line at the slant-butt junction is easy to overlook, and it is exactly the reaction that can point toward \u003Cem>Salmonella\u003C\u002Fem> Typhi. Full KIA principle, tube-reading rules, and the KIA\u002FTSI distinction explained.\u003C\u002Fp>","2019-04-30","2026-09-04",[],[82,83],"carbohydrate-utilization","h2s-production",{"slug":85,"title":86,"description":87,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":88,"lastUpdatedDate":89,"draft":46,"category":47,"image":42,"faq":90,"tags":106},"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","2026-08-05",[91,94,97,100,103],{"question":92,"answer":93},"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":95,"answer":96},"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":98,"answer":99},"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":101,"answer":102},"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":104,"answer":105},"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.",[72],{"slug":108,"title":109,"description":110,"seoTitle":111,"seoDescription":112,"author":43,"createdDate":113,"lastUpdatedDate":114,"draft":46,"category":47,"image":42,"faq":115,"tags":140},"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",[116,119,122,125,128,131,134,137],{"question":117,"answer":118},"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":120,"answer":121},"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":123,"answer":124},"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":126,"answer":127},"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":129,"answer":130},"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":132,"answer":133},"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":135,"answer":136},"\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":138,"answer":139},"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>",[72],{"slug":142,"title":143,"description":144,"seoTitle":42,"seoDescription":42,"author":145,"createdDate":146,"lastUpdatedDate":114,"draft":46,"category":47,"image":42,"faq":147,"tags":172},"casein-hydrolysis-test-principle-procedure-and-uses","Casein Hydrolysis Test: Principle, Procedure, and Uses","\u003Cp>The casein hydrolysis test detects caseinase on skim milk agar, shown by a clear zone around growth. Learn the principle, how to read the result, positive and negative organisms, and how it differs from gelatin hydrolysis.\u003C\u002Fp>","Samikshya Acharya","2022-09-04",[148,151,154,157,160,163,166,169],{"question":149,"answer":150},"\u003Cp>What does a positive casein hydrolysis test look like?\u003C\u002Fp>","\u003Cp>A clear, transparent zone around the line of growth on skim milk agar. The clearing means the organism produced caseinase and digested the casein, removing the white opacity from that part of the agar.\u003C\u002Fp>",{"question":152,"answer":153},"\u003Cp>What does a negative casein hydrolysis test look like?\u003C\u002Fp>","\u003Cp>The agar stays opaque and milk-white right up to the growth, with no clearing. This means the organism did not produce caseinase.\u003C\u002Fp>",{"question":155,"answer":156},"\u003Cp>Why does the clear zone form?\u003C\u002Fp>","\u003Cp>Casein is the protein that makes skim milk agar white and opaque. When caseinase digests the casein into soluble peptides and amino acids, the protein that was scattering light is gone, so the agar becomes clear there.\u003C\u002Fp>",{"question":158,"answer":159},"\u003Cp>Which organisms are positive and which are negative?\u003C\u002Fp>","\u003Cp>Positive organisms include \u003Cem>Bacillus\u003C\u002Fem> species, \u003Cem>Pseudomonas aeruginosa\u003C\u002Fem>, \u003Cem>Serratia marcescens\u003C\u002Fem>, and aerobic actinomycetes such as \u003Cem>Streptomyces\u003C\u002Fem>. \u003Cem>Escherichia coli\u003C\u002Fem> and \u003Cem>Enterococcus faecalis\u003C\u002Fem> are negative.\u003C\u002Fp>",{"question":161,"answer":162},"\u003Cp>What enzyme does the test detect?\u003C\u002Fp>","\u003Cp>Caseinase, also called casease. It is a protease, an enzyme that breaks the peptide bonds of casein.\u003C\u002Fp>",{"question":164,"answer":165},"\u003Cp>How long should the plate be incubated before reporting negative?\u003C\u002Fp>","\u003Cp>Hold it for at least 3 days at 35°C, and up to 14 days at 25°C for slow growers, because casein hydrolysis can be delayed. Reporting negative at 24 hours is unreliable.\u003C\u002Fp>",{"question":167,"answer":168},"\u003Cp>How is casein hydrolysis different from gelatin hydrolysis?\u003C\u002Fp>","\u003Cp>Both detect the ability to break down protein, but casein hydrolysis uses skim milk agar and shows a clear zone, while gelatin hydrolysis uses nutrient gelatin and shows the medium staying liquid after chilling. They detect different enzymes.\u003C\u002Fp>",{"question":170,"answer":171},"\u003Cp>Is the test enough to identify an organism?\u003C\u002Fp>","\u003Cp>No. It is presumptive. It narrows the possibilities but must be combined with other biochemical tests for a definitive identification.\u003C\u002Fp>",[72],{"slug":174,"title":175,"description":176,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":177,"lastUpdatedDate":114,"draft":46,"category":178,"image":42,"faq":179,"tags":204},"urea-breath-test-ubt-h-pylori-principle-procedure-results","Urea Breath Test (UBT): Principle, Procedure, and Results","\u003Cp>The urea breath test (UBT) detects active \u003Cem>Helicobacter pylori \u003C\u002Fem>infection. Learn the principle, the 13C and 14C versions, patient preparation, how the result is read (delta over baseline), and what a positive result means.\u003C\u002Fp>","2016-10-03","bacteriology",[180,183,186,189,192,195,198,201],{"question":181,"answer":182},"\u003Cp>What does a positive urea breath test mean?\u003C\u002Fp>","\u003Cp>It means active \u003Cem>Helicobacter pylori\u003C\u002Fem> infection is present. The bacterium's urease enzyme split the labeled urea and produced labeled carbon dioxide in the breath. A positive result supports treatment.\u003C\u002Fp>",{"question":184,"answer":185},"\u003Cp>What does a negative urea breath test mean?\u003C\u002Fp>","\u003Cp>It means no active infection was detected, provided the test was done with correct preparation. A negative result reliably rules out active \u003Cem>Helicobacter pylori\u003C\u002Fem> infection, but it does not assess ulcers or other stomach conditions.\u003C\u002Fp>",{"question":187,"answer":188},"\u003Cp>What is the normal range or cutoff for the urea breath test?\u003C\u002Fp>","\u003Cp>For the 13C test, the result is reported as delta over baseline (DOB). A common cutoff is greater than 4‰ for a positive result, but the exact cutoff depends on the kit, so read the result against the manufacturer's stated value. Values just above the cutoff can fall in a gray zone and may need repeating.\u003C\u002Fp>",{"question":190,"answer":191},"\u003Cp>What is the difference between the 13C and 14C urea breath tests?\u003C\u002Fp>","\u003Cp>Both work the same way. 13C is a non-radioactive isotope, is preferred, and is safe in children and pregnancy. 14C is radioactive, cheaper, and is generally avoided in children and pregnant women.\u003C\u002Fp>",{"question":193,"answer":194},"\u003Cp>Is the urea breath test safe in pregnancy?\u003C\u002Fp>","\u003Cp>The 13C test is non-radioactive and is considered safe in pregnancy and in children. The 14C test involves radiation and is avoided in these groups, so the 13C version is used instead.\u003C\u002Fp>",{"question":196,"answer":197},"\u003Cp>How should I prepare for a urea breath test?\u003C\u002Fp>","\u003Cp>Do not eat or drink for at least 4 to 6 hours before the test, do not smoke for at least 2 hours, stop antibiotics for at least 4 weeks, and stop proton pump inhibitors for at least 1 to 2 weeks. Always follow the specific instructions from the clinician and the test kit.\u003C\u002Fp>",{"question":199,"answer":200},"\u003Cp>Why must antibiotics and acid-reducing drugs be stopped first?\u003C\u002Fp>","\u003Cp>These drugs suppress the organism without necessarily eliminating it. If the test is done too soon, a suppressed but still-present infection can read falsely negative.\u003C\u002Fp>",{"question":202,"answer":203},"\u003Cp>How soon after treatment can the test confirm a cure?\u003C\u002Fp>","\u003Cp>The urea breath test can confirm eradication about 4 weeks after finishing treatment. Antibody blood tests cannot do this, because antibodies can stay positive for six months or more.\u003C\u002Fp>",[72],{"slug":206,"title":207,"description":208,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":209,"lastUpdatedDate":114,"draft":46,"category":47,"image":42,"faq":210,"tags":235},"elek-test-principle-procedure-results","Elek Test (Elek's Gel Precipitation Test): Principle, Procedure, and Results","\u003Cp>The Elek test (Elek's gel precipitation test) is an immunodiffusion test that shows whether a \u003Cem>Corynebacterium diphtheriae\u003C\u002Fem> strain produces diphtheria toxin. Learn the principle, procedure, how to read the precipitin lines, and how it compares with PCR.\u003C\u002Fp>","2015-11-23",[211,214,217,220,223,226,229,232],{"question":212,"answer":213},"\u003Cp>What is the Elek test used for?\u003C\u002Fp>","\u003Cp>It determines whether a strain of \u003Cem>Corynebacterium diphtheriae\u003C\u002Fem> produces diphtheria toxin. Only toxin-producing (toxigenic) strains cause diphtheria, so the test guides treatment and public health decisions.\u003C\u002Fp>",{"question":215,"answer":216},"\u003Cp>What is a positive Elek test?\u003C\u002Fp>","\u003Cp>The strain produces precipitin lines that join the toxigenic control's lines in a continuous arc, called a line of identity. This confirms the strain makes diphtheria toxin.\u003C\u002Fp>",{"question":218,"answer":219},"\u003Cp>What is a negative Elek test?\u003C\u002Fp>","\u003Cp>No precipitin lines form along the strain's streak. The strain does not produce the toxin.\u003C\u002Fp>",{"question":221,"answer":222},"\u003Cp>Why is it called the gel precipitation test?\u003C\u002Fp>","\u003Cp>Because the toxin and the antitoxin diffuse through the agar gel and form a visible precipitate where they meet. It is a gel-based immunoprecipitation (immunodiffusion) test.\u003C\u002Fp>",{"question":224,"answer":225},"\u003Cp>What is a line of identity?\u003C\u002Fp>","\u003Cp>It is the smooth, continuous line formed when a test strain's precipitin line joins the positive control's line. It confirms that the toxin the strain produces is the same as true diphtheria toxin.\u003C\u002Fp>",{"question":227,"answer":228},"\u003Cp>How is the Elek test different from PCR?\u003C\u002Fp>","\u003Cp>PCR detects the toxin gene (tox). The Elek test detects whether the toxin is actually produced. Some strains carry the gene but do not make the toxin, so the Elek test is used to confirm true toxin production.\u003C\u002Fp>",{"question":230,"answer":231},"\u003Cp>What are NTTB strains?\u003C\u002Fp>","\u003Cp>Non-toxigenic toxin gene-bearing strains carry the tox gene and are PCR-positive, but they do not produce the toxin and are Elek-negative. They do not cause classical diphtheria.\u003C\u002Fp>",{"question":233,"answer":234},"\u003Cp>Does finding C. diphtheriae mean the patient has diphtheria?\u003C\u002Fp>","\u003Cp>Not on its own. Only toxigenic strains cause diphtheria. The Elek test confirms whether the strain that was isolated actually produces the toxin.\u003C\u002Fp>",[72],{"slug":237,"title":238,"description":239,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":240,"lastUpdatedDate":114,"draft":46,"category":47,"image":42,"faq":241,"tags":266},"butyrate-disk-test-principle-procedure-results-uses","Butyrate Disk Test: Principle, Procedure, Results, Uses","\u003Cp>The butyrate disk test detects butyrate esterase to presumptively identify \u003Cem>Moraxella catarrhalis \u003C\u002Fem>by a blue color. Learn the principle, procedure, how to read the result, and why it matters for beta-lactamase-producing \u003Cem>M. catarrhalis.\u003C\u002Fem>\u003C\u002Fp>","2015-05-25",[242,245,248,251,254,257,260,263],{"question":243,"answer":244},"\u003Cp>What does the butyrate disk test detect?\u003C\u002Fp>","\u003Cp>It detects the enzyme butyrate esterase. When present, the enzyme hydrolyzes the substrate on the disk and releases indoxyl, which forms blue indigo.\u003C\u002Fp>",{"question":246,"answer":247},"\u003Cp>What does a positive butyrate disk test mean?\u003C\u002Fp>","\u003Cp>A blue to blue-violet color (or fluorescence with the MUB substrate) is positive. In an oxidase-positive, Gram-negative diplococcus with typical morphology, this gives a presumptive identification of \u003Cem>Moraxella catarrhalis\u003C\u002Fem>.\u003C\u002Fp>",{"question":249,"answer":250},"\u003Cp>What does a negative result mean?\u003C\u002Fp>","\u003Cp>No color change. The organism does not produce butyrate esterase. \u003Cem>Neisseria\u003C\u002Fem> species, including \u003Cem>Neisseria gonorrhoeae\u003C\u002Fem> and \u003Cem>Neisseria lactamica\u003C\u002Fem>, are butyrate-negative.\u003C\u002Fp>",{"question":252,"answer":253},"\u003Cp>Why is the butyrate test used for Moraxella catarrhalis?\u003C\u002Fp>","\u003Cp>\u003Cem>M. catarrhalis\u003C\u002Fem> looks identical to \u003Cem>Neisseria\u003C\u002Fem> species on Gram stain and oxidase testing, since all are oxidase-positive, Gram-negative diplococci. The butyrate test separates them quickly, because \u003Cem>M. catarrhalis\u003C\u002Fem> is butyrate-positive and \u003Cem>Neisseria\u003C\u002Fem> species are not.\u003C\u002Fp>",{"question":255,"answer":256},"\u003Cp>Why must the disk be read within 5 minutes?\u003C\u002Fp>","\u003Cp>Reading later than 5 minutes can give a false positive, because color develops nonspecifically over time.\u003C\u002Fp>",{"question":258,"answer":259},"\u003Cp>Can organisms other than M. catarrhalis give a positive result?\u003C\u002Fp>","\u003Cp>Yes. Some other \u003Cem>Moraxella\u003C\u002Fem> species, \u003Cem>Acinetobacter\u003C\u002Fem>, \u003Cem>Eikenella\u003C\u002Fem>, staphylococci, and pseudomonads can be positive. This is why the test is only interpreted on an oxidase-positive, Gram-negative diplococcus with typical morphology.\u003C\u002Fp>",{"question":261,"answer":262},"\u003Cp>What should I do if the organism looks like M. catarrhalis but tests negative?\u003C\u002Fp>","\u003Cp>Repeat with a heavier inoculum, since a small inoculum can cause a false negative. If it is still negative but fits the other criteria, DNase testing can be used as a further confirmatory step.\u003C\u002Fp>",{"question":264,"answer":265},"\u003Cp>Does a positive butyrate test tell me about antibiotic resistance?\u003C\u002Fp>","\u003Cp>Not directly, but identifying \u003Cem>M. catarrhalis\u003C\u002Fem> is a strong hint, because most strains produce beta-lactamase and resist penicillin and ampicillin. Beta-lactamase is confirmed separately with the nitrocefin test.\u003C\u002Fp>",[72],{"slug":268,"title":269,"description":270,"seoTitle":271,"seoDescription":272,"author":43,"createdDate":273,"lastUpdatedDate":274,"draft":46,"category":47,"image":42,"faq":275,"tags":297},"api-20e-test-system-introduction-procedure-results-interpretations","API 20E Test: Procedure, Reading the 21 Reactions, and the 7-Digit Profile Code","How to set up, incubate, and read the API 20E strip: which wells need oil, which need reagents, how to run the 21st test (oxidase), and how to build the 7-digit profile number for identification.","API 20E: Inoculation, Reading, Profile Number, and Identification","Prepare and inoculate an API 20E strip, add reagents, read biochemical reactions, calculate the profile number, and interpret organism identification.","2015-05-06","2026-08-22",[276,279,282,285,288,291,294],{"question":277,"answer":278},"How many tests are in the API 20E, 20 or 21?","The strip has 20 wells, but a complete identification uses 21 reactions. The oxidase test is performed separately, off the strip, and fills the last position in the profile code.",{"question":280,"answer":281},"Which API 20E wells need a mineral oil overlay?","Five: ADH, LDC, ODC, URE, and H₂S. The oil creates the anaerobic conditions these reactions need. Without it, they read falsely.",{"question":283,"answer":284},"Which wells need reagents added after incubation?","Three: TDA (ferric chloride), IND (Kovács' reagent), and VP (KOH followed by α-naphthol). Add these only after reading every self-developing well.",{"question":286,"answer":287},"Why does the VP well take longer to read?","The pink-red color from acetoin detection can take up to 10 minutes to develop. Do not call VP negative before then. TDA and IND, by contrast, are read almost immediately.",{"question":289,"answer":290},"How is the 7-digit profile number generated?","The 21 reactions are grouped into seven triplets. Within each triplet the wells score 1, 2, and 4 from top to bottom; you add up only the positives, giving a digit from 0 to 7. The seven digits form the profile, which you look up in apiweb or the API catalog.",{"question":292,"answer":293},"What do I do if the profile gives a doubtful or low-confidence identification?","apiweb reports a %ID and a T-value; a low or non-discriminating result means you need supplementary tests (such as oxidase, nitrate reduction, or motility) or a repeat run, rather than accepting the closest match.",{"question":295,"answer":296},"Can API 20E identify organisms other than Enterobacteriaceae?","It is designed for Enterobacteriaceae and other non-fastidious Gram-negative rods. It is not suitable for fastidious organisms or non-fermenters outside its database scope, which need different panels.",[82,72,298],"substrate-utilization",{"enabled":300,"threads":301,"total":302},true,[],0,[304,310,317,324,329,334,340,345,351,354,361],{"slug":305,"name":43,"description":306,"image":307,"body":308,"postCount":309},"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.*",516,{"slug":311,"name":312,"description":313,"image":314,"body":315,"postCount":316},"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.",88,{"slug":318,"name":319,"description":320,"image":321,"body":322,"postCount":323},"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":325,"name":145,"description":320,"image":326,"body":327,"postCount":328},"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":330,"name":331,"description":320,"image":42,"body":332,"postCount":333},"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":335,"name":336,"description":337,"image":42,"body":338,"postCount":339},"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":341,"name":342,"description":343,"image":42,"body":42,"postCount":344},"guest-author","Guest Author","Guest Author \u002F Contributor",1,{"slug":346,"name":347,"description":320,"image":348,"body":349,"postCount":350},"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":352,"name":353,"description":343,"image":42,"body":42,"postCount":344},"dr-poonam-acharya","Dr. Poonam Acharya",{"slug":355,"name":356,"description":357,"image":358,"body":359,"postCount":360},"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.*",55,{"slug":362,"name":363,"description":364,"image":365,"body":366,"postCount":344},"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.",[368,375,381,385,390,395,399,403,407,412,416,421,425,430,435,440,444,448,453,458,462,466,470,474,478,482,486,490,495,500,505,509,513,518,522,526,530,534,538,542,546,550,554,557,561,566,570,574,579,583,587,591,595,599,602,606,610,614,617,621,625,629,633,637,641,645,649,653,656,660,663,666,669,672,675,678,681,684,686,689,692,695,698,701,704,707,711,714],{"slug":369,"name":370,"description":371,"image":372,"body":373,"postCount":374},"gram-negative-cocci","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":376,"name":377,"description":378,"image":42,"body":379,"postCount":380},"microscopy","Microscopy","Microscope types, components, and microscopy techniques","These are list of blog posts related to microscopy. ",12,{"slug":382,"name":383,"description":384,"image":42,"body":42,"postCount":380},"gram-positive-cocci","Gram-Positive Cocci","Staphylococcus, Streptococcus, Enterococcus, Micrococcus — organisms, diseases, and identification tests",{"slug":386,"name":387,"description":388,"image":42,"body":42,"postCount":389},"gram-negative-rods","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":391,"name":392,"description":393,"image":42,"body":42,"postCount":394},"gram-positive-rods","Gram-Positive Rods","Bacillus, Clostridium, Listeria, Corynebacterium, Actinomyces and related organisms",8,{"slug":396,"name":397,"description":398,"image":42,"body":42,"postCount":380},"mycobacteria","Mycobacteria","Mycobacterium tuberculosis, leprosy, atypical mycobacteria, and acid-fast organism diagnosis",{"slug":400,"name":401,"description":402,"image":42,"body":42,"postCount":380},"anaerobic-bacteriology","Anaerobic Bacteriology","Anaerobic organisms, anaerobic culture methods, and anaerobic infection diagnosis",{"slug":404,"name":405,"description":406,"image":42,"body":42,"postCount":380},"enterobacteriaceae","Enterobacteriaceae","Identification, differentiation, and clinical significance of Enterobacteriaceae family members",{"slug":408,"name":409,"description":410,"image":42,"body":42,"postCount":411},"spirochetes","Spirochetes","Treponema, Leptospira, Borrelia and spirochetal infections",7,{"slug":413,"name":414,"description":415,"image":42,"body":42,"postCount":374},"food-microbiology","Food Microbiology","Food-borne pathogens, food safety, spoilage, and preservation",{"slug":417,"name":418,"description":419,"image":42,"body":42,"postCount":420},"antimicrobial-susceptibility-testing","Antimicrobial Susceptibility Testing","Methods for testing antibiotic susceptibility in clinical microbiology",22,{"slug":422,"name":423,"description":424,"image":42,"body":42,"postCount":374},"antimicrobials-moa-amr","Antimicrobials (MOA & AMR)","Mechanisms, detection, and clinical significance of antimicrobial resistance",{"slug":426,"name":427,"description":428,"image":42,"body":42,"postCount":429},"sterilization-disinfection","Sterilization and Disinfection","Methods of sterilization and disinfection in healthcare and laboratory settings",10,{"slug":431,"name":432,"description":433,"image":42,"body":42,"postCount":434},"specimen-collection-transport","Specimen Collection and Transport","Collection, handling, and transport of clinical specimens for microbiological testing",27,{"slug":436,"name":437,"description":438,"image":42,"body":42,"postCount":439},"bacterial-structure-physiology","Bacterial Structure and Physiology","Bacterial cell structure, growth, physiology, and environmental factors affecting growth",21,{"slug":441,"name":442,"description":42,"image":42,"body":443,"postCount":333},"horizontal-gene-transfer","Horizontal Gene Transfer","Articles related to **Horizontal Gene Transfer**",{"slug":445,"name":446,"description":42,"image":42,"body":447,"postCount":429},"chromatography","Chromatography","Information about chromatographic techniques.",{"slug":449,"name":450,"description":451,"image":42,"body":452,"postCount":411},"electrophoresis","Electrophoresis","Information about Electrophoresis Techniques ","Detailed information  about Electrophoresis Techniques ",{"slug":454,"name":455,"description":456,"image":42,"body":457,"postCount":333},"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":459,"name":460,"description":461,"image":42,"body":42,"postCount":333},"bacteriophage","Bacteriophage","Description about Bacteriophage.",{"slug":463,"name":464,"description":465,"image":42,"body":42,"postCount":333},"malaria","Malaria","It is the collections of articles regarding malarial disease. ",{"slug":467,"name":468,"description":469,"image":42,"body":42,"postCount":333},"anaerobic-culture-techniques","Anaerobic Culture Techniques","Posts related with Anaerobic Culture Techniques.",{"slug":471,"name":472,"description":473,"image":42,"body":42,"postCount":439},"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.",{"slug":475,"name":476,"description":477,"image":42,"body":42,"postCount":411},"biosafety-levels","Biosafety levels ","Articles related to Biosafety Levels",{"slug":479,"name":480,"description":481,"image":42,"body":42,"postCount":389},"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":483,"name":484,"description":485,"image":42,"body":42,"postCount":333},"pipette","Pipette","Posts related with Pipette. ",{"slug":487,"name":488,"description":489,"image":42,"body":42,"postCount":411},"bacteriology-mcqs","Bacteriology MCQs","This sections lists MCQs in Bacteriology.",{"slug":491,"name":492,"description":493,"image":42,"body":42,"postCount":494},"parasitology-mcqs","Parasitology MCQs","This section lists MCQs in Parasitology.",2,{"slug":496,"name":497,"description":498,"image":42,"body":42,"postCount":499},"virology-mcqs","Virology MCQs","This is the collections of Multiple Choice Questions in Virology.",4,{"slug":501,"name":502,"description":503,"image":42,"body":42,"postCount":504},"mcqs-in-microbiology","MCQs in Microbiology","This section lists the collections of Multiple Choice Questions in General Microbiology Topics. ",3,{"slug":506,"name":507,"description":508,"image":42,"body":42,"postCount":411},"immunology-mcqs","Immunology MCQs","In this section; we are posting collections of Multiple Choice Questions about Immunology. ",{"slug":510,"name":511,"description":512,"image":42,"body":42,"postCount":429},"microbial-curiosities","Microbial Curiosities","In this clusters, we are posting interesting and unique information about Microorganisms. ",{"slug":514,"name":515,"description":516,"image":42,"body":42,"postCount":517},"bacterial-culture-media","Bacterial Culture Media","Posts related to Bacterial Culture Media. ",23,{"slug":519,"name":520,"description":521,"image":42,"body":42,"postCount":333},"fungal-culture-media","Fungal Culture Media","Posts related to Fungal Culture Media.",{"slug":523,"name":524,"description":525,"image":42,"body":42,"postCount":389},"motility-test","Motility Test","This lists the procedure regarding various tests methods for bacterial motility.",{"slug":527,"name":528,"description":529,"image":42,"body":42,"postCount":429},"bacterial-enumeration","Bacterial enumeration","These posts are related to isolation and enumeration of bacteria. ",{"slug":531,"name":532,"description":533,"image":42,"body":42,"postCount":494},"gram-positive-coccobacillus","Gram-positive coccobacillus","List of Gram Positive Coccobacilli",{"slug":535,"name":536,"description":537,"image":42,"body":42,"postCount":333},"dimorphic-fungi","Dimorphic Fungi","This is about various dimorphic fungi. ",{"slug":539,"name":540,"description":541,"image":42,"body":42,"postCount":411},"bacterial-classification","Bacterial Classification","These posts are related with various approaches used for the classification of Bacteria. ",{"slug":543,"name":544,"description":545,"image":42,"body":42,"postCount":389},"immunofluorescence","Immunofluorescence ","Various Tests related to Immunofluorescence ",{"slug":547,"name":548,"description":549,"image":42,"body":42,"postCount":339},"antibody-mediated-immunity","Antibody-mediated Immunity","This clusters links the articles that are sharing insights about Antibody-mediated immunity. ",{"slug":551,"name":552,"description":553,"image":42,"body":42,"postCount":411},"hypersensitivity","Hypersensitivity","Articles related to Hypersensitivity.",{"slug":555,"name":556,"description":42,"image":42,"body":42,"postCount":504},"haemophilus","Haemophilus",{"slug":558,"name":559,"description":560,"image":42,"body":42,"postCount":333},"sexually-transmitted-infections-stis","Sexually transmitted infections (STIs)","This is the clusters of infections that are transmitted sexually. ",{"slug":562,"name":563,"description":564,"image":42,"body":42,"postCount":565},"adaptive-immunity","Adaptive Immunity","Blog posts related to B Cell Immunity and T Cell Immunity.",13,{"slug":567,"name":568,"description":569,"image":42,"body":42,"postCount":374},"fungal-diagnostics","Fungal Diagnostics","Various methods used for the Diagnosis of Fungal Infections. ",{"slug":571,"name":572,"description":573,"image":42,"body":42,"postCount":389},"laboratory-storage-and-preservation","Laboratory Storage and Preservation","Articles about Laboratory Storage of Antimicrobial Disk, Test organisms and Equipment used for this process. ",{"slug":575,"name":576,"description":577,"image":42,"body":578,"postCount":333},"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":580,"name":581,"description":582,"image":42,"body":42,"postCount":339},"laboratory-glassware","Laboratory Glassware","Posts about Laboratory Glassware. ",{"slug":584,"name":585,"description":586,"image":42,"body":42,"postCount":339},"helminths","Helminths","In this section, we are covering properties, life cycle, pathogenesis and laboratory diagnosis of Helminths\u002FHelminthic infestations. ",{"slug":588,"name":589,"description":590,"image":42,"body":42,"postCount":333},"protozoan-parasite","Protozoan Parasite","In this cluster, we are covering protozoan parasites. ",{"slug":592,"name":593,"description":594,"image":42,"body":42,"postCount":344},"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":596,"name":597,"description":598,"image":42,"body":42,"postCount":429},"bacterial-staining-technique","Bacterial Staining Technique","Lists of various staining techniques that are used to stain bacteria. ",{"slug":72,"name":600,"description":601,"image":42,"body":42,"postCount":439},"Enzyme Tests","\u003Cp>Various Biochemical Test that are based on enzymatic activity of the microorganisms. \u003C\u002Fp>",{"slug":82,"name":603,"description":604,"image":42,"body":42,"postCount":605},"Carbohydrate Utilization","\u003Cp>Various biochemical tests which are related to Carbohydrate fermentation or Utilization\u003C\u002Fp>",11,{"slug":607,"name":608,"description":609,"image":42,"body":42,"postCount":389},"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":42,"body":42,"postCount":499},"microbial-metabolism","Microbial Metabolism","\u003Cp>Tests about Microbial Metabolism. \u003C\u002Fp>",{"slug":298,"name":615,"description":616,"image":42,"body":42,"postCount":394},"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":618,"name":619,"description":620,"image":42,"body":42,"postCount":504},"atypical-pneumonia","Atypical Pneumonia","\u003Cp>Organisms responsible for Atypical Pneumonia. \u003C\u002Fp>",{"slug":622,"name":623,"description":624,"image":42,"body":42,"postCount":389},"antigen","Antigen","\u003Cp>Various articles related to Antigens.\u003C\u002Fp>",{"slug":626,"name":627,"description":628,"image":42,"body":42,"postCount":411},"innate-immunity","Innate Immunity","\u003Cp>Articles related to Innate Immunity. \u003C\u002Fp>",{"slug":630,"name":631,"description":632,"image":42,"body":42,"postCount":499},"respiratory-tract-infection","Respiratory Tract Infection","\u003Cp>In this cluster, you can see various etiological agents that causes respiratory tract infection. \u003C\u002Fp>",{"slug":634,"name":635,"description":636,"image":42,"body":42,"postCount":389},"torch-infection","TORCH Infection","\u003Cp>In this section; you can find articles related with TOCH infection. \u003C\u002Fp>",{"slug":638,"name":639,"description":640,"image":42,"body":42,"postCount":394},"microbiology-for-beginners","Microbiology for Beginners","\u003Cp>These articles are very basic articles, which will share general concepts in Microbiology. \u003C\u002Fp>",{"slug":642,"name":643,"description":644,"image":42,"body":42,"postCount":333},"dna-replication","DNA Replication","\u003Cp>Articles related to DNA and Replication of DNA. \u003C\u002Fp>",{"slug":646,"name":647,"description":648,"image":42,"body":42,"postCount":333},"genetic-code","Genetic Code","\u003Cp>Articles related to Genetic Code.\u003C\u002Fp>",{"slug":650,"name":651,"description":652,"image":42,"body":42,"postCount":411},"molecular-technique","Molecular Technique","\u003Cp>Posts related to Molecular Techniques. \u003C\u002Fp>",{"slug":654,"name":655,"description":42,"image":42,"body":42,"postCount":344},"colorimetric-assay","Colorimetric Assay ",{"slug":657,"name":658,"description":659,"image":42,"body":42,"postCount":389},"pharmaceutical-microbiology","Pharmaceutical Microbiology","\u003Cp>Various articles related to Pharmaceutical Microbiology\u003C\u002Fp>",{"slug":661,"name":662,"description":42,"image":42,"body":42,"postCount":504},"blood-and-immune-cells","Blood and Immune Cells",{"slug":664,"name":665,"description":42,"image":42,"body":42,"postCount":389},"host-pathogen-interaction","Host Pathogen Interaction",{"slug":667,"name":668,"description":42,"image":42,"body":42,"postCount":499},"blood-culture","Blood Culture",{"slug":670,"name":671,"description":42,"image":42,"body":42,"postCount":499},"environmental-microbiology","Environmental microbiology ",{"slug":673,"name":674,"description":42,"image":42,"body":42,"postCount":411},"copromicroscopic-technique","Copromicroscopic Technique",{"slug":676,"name":677,"description":42,"image":42,"body":42,"postCount":504},"quality-control","Quality Control",{"slug":679,"name":680,"description":42,"image":42,"body":42,"postCount":411},"dermatophytes","Dermatophytes",{"slug":682,"name":683,"description":42,"image":42,"body":42,"postCount":504},"viral-hemorrhagic-fevers","Viral Hemorrhagic Fevers",{"slug":83,"name":685,"description":42,"image":42,"body":42,"postCount":499},"H2S Production",{"slug":687,"name":688,"description":42,"image":42,"body":42,"postCount":494},"water-quality-testing","Water Quality Testing",{"slug":690,"name":691,"description":42,"image":42,"body":42,"postCount":389},"virology-basics","Virology basics",{"slug":693,"name":694,"description":42,"image":42,"body":42,"postCount":499},"typing-methods","Typing Methods",{"slug":696,"name":697,"description":42,"image":42,"body":42,"postCount":504},"blotting-technique","Blotting Technique",{"slug":699,"name":700,"description":42,"image":42,"body":42,"postCount":499},"history-microbiology","History of Microbiology",{"slug":702,"name":703,"description":42,"image":42,"body":42,"postCount":333},"trematodes","Trematodes",{"slug":705,"name":706,"description":42,"image":42,"body":42,"postCount":499},"coccidian-parasites","Coccidian Parasites",{"slug":708,"name":709,"description":710,"image":42,"body":42,"postCount":374},"cell-structure","Cell Structure","\u003Cp>Articles related to Cell Structure. \u003C\u002Fp>",{"slug":712,"name":713,"description":42,"image":42,"body":42,"postCount":302},"automation-in-microbiology","Automation in Microbiology",{"slug":715,"name":716,"description":42,"image":42,"body":42,"postCount":333},"laboratory-management","Laboratory Management"]