[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$f7iTaqgMnOgQLQtPDdA_M-EV4wIsC_D-ft1mX92bn29o":36,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":288,"$fucxFBm2ZjZfGSdmdRaSNGBI_F0jJme4f0GTvzUhQfL8":351},[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":284},"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>",null,"Acharya Tankeshwar","2013-08-23","2026-08-22",false,"culture-media","A water quality inspector sends a sample from a municipal tap to the laboratory, concerned about fecal contamination following recent flooding. The technician plates the sample onto EMB agar. Within 24 hours, colonies with a striking metallic green sheen appear under reflected light: the unmistakable signature of *Escherichia coli*, a confirmed indicator of fecal contamination.\n\nThat metallic green sheen is one of the most distinctive colony appearances in all of bacteriology, and it is produced only by organisms that ferment lactose so vigorously that the acidified medium causes eosin and methylene blue dyes to combine into a dark precipitate that reflects green light.\n\nEMB agar is used wherever you need to (1) select for Gram-negative enteric organisms, and (2) immediately distinguish the vigorous lactose fermenters (the fecal coliforms) from everything else.\n\n**Introduction**\n\nEosin Methylene Blue (EMB) agar is a selective and differential culture medium. It selectively promotes the growth of Gram-negative bacteria and aids in the differentiation of lactose fermenter and non-lactose fermenting colonies.\n\nEMB Agar is used for the isolation of fecal coliforms. EMB Agar can be streaked for isolation or used in the [Membrane Filter Technique](https:\u002F\u002Fmicrobeonline.com\u002Fanalysis-of-water-membrane-filtration-technique\u002F). EMB agar inoculated with *Escherichia coli* demonstrates growth with green-metallic sheen colonies.\n\n![EMB Agar - Escherichia colicolonies in Eosin Methylene Blue Agar(Note: Greenish Metallic Sheen)](\u002Fblogs\u002Femb-Agar.jpg)Figure: *Escherichia coli* colonies in Eosin Methylene Blue Agar (Note: Greenish Metallic Sheen)\n\nEMB agar, first described by Holt-Harris and Teague, contained lactose and sucrose as sources of carbohydrates. Levine modified the medium by adding peptone and phosphate, removing sucrose from the formula, and increasing the lactose content. This aided in differentiating fecal and non-fecal types of coliforms. It also differentiates salmonellae and other non-lactose fermenters from the coliforms.\n\nEMB agar serves two simultaneous purposes: **selection** and **differentiation**, making it one of the most informative primary plating media in clinical microbiology:\n\n- **Selective:** Eosin Y and methylene blue dyes inhibit gram-positive organisms and most fastidious gram-negative bacteria, allowing gram-negative enteric bacilli to grow\n- **Differential:** Lactose as the fermentable sugar, with eosin and methylene blue as pH-sensitive dyes, produces dramatically different colony appearances depending on how vigorously an organism ferments it, ranging from the metallic green sheen of vigorous fermenters to the colorless colonies of non-fermenters\n\n> Another commonly used media for selective isolation of Gram-negative rods and differentiation of the member of Enterobacteriaceae as lactose fermenter and non-lactose fermenter is MacConkey Agar.\n\n## Principle\n\nEMB agar contains lactose as the fermentable carbohydrate. The original Holt-Harris and Teague formulation also contained sucrose, but the Levine modification used in most laboratories today removes sucrose and doubles the lactose. Differentiation depends on how vigorously an organism ferments the available sugar and therefore how much acid it produces at the colony surface.\n\n- **Lactose-fermenting** gram-negative bacteria acidify the medium, which reduces the pH, and the dye produces a **dark purple complex usually associated with a green metallic sheen.** This metallic green sheen indicates the vigorous lactose fermentation typical of fecal coliforms.\n- Organisms that are **slow lactose-fermenters** produce less acid, and th**e colonies appear brown-pink.**\n- **Non-lactose fermenters** increase the pH of the medium by deamination of proteins and produce **colorless or light pink colonies.**\n\n**Eosin Y and methylene blue are pH indicator** dyes that combine to form a dark purple precipitate at low pH; they also inhibit the growth of most Gram-positive organisms. Peptic digest of animal tissue is a source of carbon, nitrogen, and other essential growth nutrients. Phosphate buffers the medium.\n\n### Why E. coli produces metallic green sheen\n\nThe characteristic metallic green sheen of *E. coli* on EMB agar is one of the most recognizable and diagnostically significant colony appearances in microbiology. Understanding why it occurs requires understanding the chemistry of the dye complex:\n\n*E. coli* is a vigorous fermenter of lactose. This fermentation produces so much acid that the pH drops dramatically at the colony surface. At this very low pH:\n\n1. Eosin Y and methylene blue precipitate out of solution and are absorbed in large quantities by the colony\n2. The massive dye complex formed at very low pH produces a dark purple-black colony color\n3. The surface of the colony develops a **metallic iridescence** due to light interference from the densely packed dye crystals, similar to the iridescent sheen seen on a soap bubble or oil film on water\n\nThis metallic green sheen is therefore a direct indicator of **vigorous acid production from lactose fermentation**, a hallmark of *E. coli* among the [*Enterobacteriaceae*](https:\u002F\u002Fmicrobeonline.com\u002Fenterobacteriaceae\u002F). On the original sucrose-containing formulation, sucrose fermenters could also produce a sheen, which is precisely why Levine removed it. Organisms that ferment lactose less vigorously (like *Klebsiella*) may produce dark colonies but without the metallic sheen.\n\n## Composition of EMB Agar\n\nThe original EMB agar (Holt-Harris and Teague) contained both lactose and sucrose. Levine modified the formula by removing sucrose and doubling the lactose content: this modification reduces the number of false-positive metallic sheen colonies from sucrose-only fermenters and improves discrimination of true fecal coliforms. **Levine EMB is the formulation used in most clinical and water microbiology laboratories today.**\n\n\u003Ctable style=\"min-width: 75px;\">\n\u003Ccolgroup>\u003Ccol style=\"min-width: 25px;\">\u003Ccol style=\"min-width: 25px;\">\u003Ccol style=\"min-width: 25px;\">\u003C\u002Fcolgroup>\u003Ctbody>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cstrong>Ingredients\u003C\u002Fstrong>\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cstrong>EMB agar (gm\u002FL)\u003C\u002Fstrong>\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cstrong>Levine EMB agar (gm\u002FL)\u003C\u002Fstrong>\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Peptone\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>10 g\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>10g\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Lactose\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>5 g\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>10g\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Sucrose\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>5g\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>–\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Dipotassium phosphate (K₂HPO₄)\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>2g\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>2g\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Ca target=\"_blank\" rel=\"noopener noreferrer\" href=\"https:\u002F\u002Fmicrobeonline.com\u002Fagar-properties-uses\u002F\">\u003Cu>Agar\u003C\u002Fu>\u003C\u002Fa>\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>13.5g\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>13.5g\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Eosin Y\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>0.4g\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>0.4g\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Methylene blue\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>0.065g\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>0.065g\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\npH: 7.1 ± 0.2 at 25 °C.\n\n**Why two dyes?** Eosin Y alone would give a reddish precipitate. Methylene blue alone would give a blue one. Together, at acidic pH, they form a dark purple-black complex that has the unique property of creating a metallic green sheen when the precipitate is dense enough (as in vigorous fermentation). The combination is synergistic: neither dye alone produces the metallic sheen.\n\n## Preparation of EMB agar\n\n1. Weigh and suspend 35.96 grams of dehydrated media in 1000 mL distilled water.\n2. Mix until the suspension is uniform and heat to boiling to dissolve the medium completely.\n3. [Sterilize by autoclaving](https:\u002F\u002Fmicrobeonline.com\u002Fautoclave-principle-procedure-types-and-uses\u002F) at 15 lbs pressure (121°C) for 15 minutes.\n4. Cool to 45-50°C, and with frequent gentle swirling, pour the media into sterile [Petri plates](https:\u002F\u002Fmicrobeonline.com\u002Fpetri-dish-types-uses-and-automated-petri-dish-filler\u002F).\\\n   \\\n   Note: frequent swirling is recommended to restore the blue color of methylene blue and to suspend the flocculent precipitate, *if any.*\n5. Label with initials of the name of the medium, and the date of preparation.\n6. Store the plates upside down (lids below) in the [refrigerator](https:\u002F\u002Fmicrobeonline.com\u002Flaboratory-refrigerator-temperature-and-storage\u002F) until use.\n\n### Inoculation and Incubation\n\n1. Allow the plate to reach room temperature and dry the agar surface before use.\n2. Inoculate directly from the specimen. Suitable specimens include urine, stool, wound swabs, and, in water microbiology, the membrane filter after filtering a measured water volume.\n3. If culturing from [a swab](https:\u002F\u002Fmicrobeonline.com\u002Ftypes-of-swabs\u002F), roll the swab over a small area at the edge of the plate first, then streak out for isolation with [a sterile loop](https:\u002F\u002Fmicrobeonline.com\u002Finoculating-loop-types-and-uses\u002F).\n4. Incubate aerobically at 35 to 37°C. EMB does not require carbon dioxide.\n5. Read at 18 to 24 hours for the primary result, and again at 48 hours. Late lactose fermenters such as *Citrobacter freundii* and *Shigella sonnei* can appear colorless or pale at 24 hours and darken by 48 hours, so an early-only read can misclassify a fermenter as a non-fermenter.\n6. For the membrane filter technique in water testing, place the filter on the EMB surface and count metallic-sheen colonies at 24 to 48 hours as presumptive fecal coliforms.\n\n### Reading on EMB plate\n\n![ - EMB agar inoculated withEscherichia colidemonstrating growth with green-metallic sheen colonies. (Image source:Carmen Moreno González)](\u002Fblogs\u002FEscherichia-coli-in-EMB-Agar.jpg)Figure: EMB agar inoculated with *Escherichia coli* demonstrating growth with green-metallic sheen colonies. (Image source: Carmen Moreno González)\n\nExamine the plate in reflected light (room light shining down onto the plate surface) for metallic sheen. Then hold the plate up to a transmitted light source (light shining through from below) to see the dark centers. Missing the reflected light step is the most common cause of misread EMB plates: colonies that show metallic green sheen only in reflected light may appear simply as dark colonies in transmitted light.\n\n## Quality Control of EMB agar\n\nSterility testing can be performed by incubating 3 to 5 uninoculated plates from each batch at 35 to 37°C for 18-24 hours. Any growth in the media should be regarded as contamination, and the whole lot should be discarded.\n\n\u003Ctable style=\"min-width: 50px;\">\n\u003Ccolgroup>\u003Ccol style=\"min-width: 25px;\">\u003Ccol style=\"min-width: 25px;\">\u003C\u002Fcolgroup>\u003Ctbody>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cstrong>\u003Cem>Organism\u003C\u002Fem>\u003C\u002Fstrong>\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cstrong>\u003Cem>Growth and colony characteristics\u003C\u002Fem>\u003C\u002Fstrong>\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cem>E. coli \u003C\u002Fem>ATCC 25922\u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Good growth\u003Cem>,\u003C\u002Fem> blue-black colonies with a green metallic sheen\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cem>Salmonella enterica\u003C\u002Fem> subsp. \u003Cem>enterica\u003C\u002Fem> serovar Typhimurium ATCC 14028\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Luxuriant growth, colorless to amber colonies\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cem>Enterococcus faecalis\u003C\u002Fem> ATCC 29212\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Inhibition (partial)\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003Ctr>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>\u003Cem>Shigella flexneri\u003C\u002Fem> ATCC 12022\u003C\u002Fp>\u003C\u002Ftd>\u003Ctd colspan=\"1\" rowspan=\"1\">\u003Cp>Moderate to heavy growth, colorless to amber colonies\u003C\u002Fp>\u003C\u002Ftd>\u003C\u002Ftr>\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\nPerformance testing of prepared EMB agar plates can be done by inoculating known strains of bacteria into the medium and observing growth and colonial characteristics.\n\n## Colony Morphology on EMB Agar\n\n### Strong lactose fermenters (dark colonies with metallic sheen)\n\n| Organism | Colony appearance | Key features |\n| --- | --- | --- |\n| *Escherichia coli* | Small to medium (2–3 mm), dark purple-black with characteristic **metallic green sheen**; flat, dry, with irregular edge | Metallic green sheen is the hallmark of vigorous acid production from lactose fermentation; most reliable presumptive indicator of *E. coli* |\n\n### Moderate lactose fermenters (dark pink to brown-pink colonies, no sheen)\n\n| Organism | Colony appearance | Key features |\n| --- | --- | --- |\n| *Klebsiella pneumoniae* | Large (4–6 mm), dark pink to brown-pink, very mucoid, dome-shaped; no metallic sheen | Mucoid capsule produces glistening, dome-shaped appearance; may string when touched |\n| *Klebsiella aerogenes* (formerly *Enterobacter aerogenes*) | Dark brown-pink center, large and mucoid, 3–4 mm; no metallic sheen | Ferments lactose but less vigorously than *E. coli*, so acid production is insufficient for the dense dye precipitate that produces the sheen |\n| *Klebsiella oxytoca* | Similar to *K. pneumoniae*: large, mucoid, dark pink-brown | Distinguished from *K. pneumoniae* by indole positivity |\n| *Enterobacter cloacae* | Dark pink, slightly mucoid; 2–3 mm | Smaller and less mucoid than *Klebsiella*; may have slightly darker center |\n| *Serratia marcescens* | Pink-brown at 37°C; may show red\u002Fpink pigment (prodigiosin) at room temperature | Distinguished by DNase positivity and prodigiosin pigment at 25°C |\n| *Citrobacter freundii* | Pale pink at 24 hours (late fermenter); darker at 48 hours | Late lactose fermentation, may appear NLF at 24 hours; H₂S positive on TSI |\n\n### Non-lactose fermenters (colorless or transparent colonies)\n\n| Organism | Colony appearance | Key features |\n| --- | --- | --- |\n| *Salmonella* Typhi | Colorless to pale pink, translucent, convex; 1–2 mm | Small, non-mucoid; no distinctive features on EMB, TSI needed for definitive direction |\n| *Salmonella* spp. (non-typhoidal) | Colorless to pale pink, convex, smooth; 2–3 mm | Cannot distinguish from *Shigella* by EMB alone |\n| *Shigella* spp. | Colorless, flat, translucent; 1–2 mm; slightly irregular edge | *S. sonnei* may show faint pink at 48 hours (late lactose fermenter) |\n| *Proteus mirabilis* | Colorless, spreading; characteristic foul odor; reduced swarming on EMB compared to blood agar | Swarming is reduced on EMB, though less reliably than on MacConkey, which contains bile salts |\n| *Proteus vulgaris* | Colorless, spreading; similar to *P. mirabilis* | Indole positive; distinguished biochemically |\n| *Pseudomonas aeruginosa* | Colorless to pale, irregular, spreading; may show blue-green pigmentation (pyocyanin); characteristic grape-like odor | Non-fermenter; oxidase positive; characteristic sweet grape odor |\n| *Acinetobacter baumannii* | Colorless to pale, opaque, convex; 1.5–2 mm | Non-fermenter; oxidase negative; important MDR nosocomial pathogen |\n| *Morganella morganii* | Colorless, flat; 2–3 mm | Urease positive; phenylalanine deaminase positive |\n\n### Organisms inhibited: no growth on EMB agar\n\n| Organism | Why inhibited |\n| --- | --- |\n| *Staphylococcus aureus* | Inhibited by eosin Y and methylene blue dyes |\n| *Streptococcus* spp. | Inhibited by dyes |\n| *Enterococcus* spp. | Inhibited by dyes |\n| *Neisseria gonorrhoeae* | Fastidious gram-negative which is inhibited by dye concentration |\n| *Haemophilus influenzae* | Fastidious, requires X and V factors not present |\n| *Campylobacter* spp. | Fastidious, requires microaerophilic conditions and selective supplements |\n\n## Uses of EMB agar\n\n**1. Isolation and differentiation of Gram-negative enteric organisms** EMB is used as a primary plating medium for clinical specimens where Gram-negative enteric organisms are expected: urine, stool, and wound specimens. It selects for Gram-negatives while simultaneously differentiating lactose fermenters (including *E. coli* and *Klebsiella*) from non-fermenters (*Salmonella*, *Shigella*).\n\n**2. Water quality testing (fecal coliform detection)** EMB agar is the standard confirmatory medium for detecting fecal coliforms in drinking water, sewage, and food samples. Samples that produce metallic green sheen colonies on EMB after positive presumptive [MPN (Most Probable Number) tests](https:\u002F\u002Fmicrobeonline.com\u002Fprobable-number-mpn-test-principle-procedure-results\u002F) confirm the presence of *E. coli*, a definitive fecal contamination indicator.\n\n**3. Differentiation of *E. coli* from other coliforms** Among lactose-fermenting Gram-negatives, the metallic green sheen specifically identifies *E. coli* (vigorous fermenter) from *Enterobacter\u002FKlebsiella* (moderate fermenter, mucoid, no sheen). This distinction is important because *E. coli* in urine is always clinically significant, while *Enterobacter* may represent colonization rather than infection.\n\n**4. Colon-typhoid-dysentery group differentiation** EMB is used alongside MacConkey agar for selective isolation of *Salmonella* and *Shigella* from stool specimens. The colorless colonies of these non-fermenters on EMB are picked for confirmatory TSI and serology.\n\n**5. *Candida* isolation (modified Levine EMB)** Levine EMB with chlortetracycline (0.1 g\u002FL added after autoclaving) suppresses bacterial flora and supports *Candida albicans* isolation, which produces characteristic \"spidery\" or \"feathery\" colonies under CO₂ conditions.\n\n## EMB Agar vs MacConkey Agar\n\nBoth EMB and MacConkey are selective and differential media for gram-negative enteric organisms, and they are frequently used together in a primary plating battery. Understanding their differences helps choose the right medium for each application:\n\n| Feature | EMB Agar | MacConkey Agar |\n| --- | --- | --- |\n| Selective agents | Eosin Y + methylene blue dyes | Crystal violet + bile salts |\n| Sugars | Lactose only (Levine); lactose + sucrose (original formulation) | Lactose only |\n| pH indicator | Eosin Y + methylene blue (change from clear to dark at low pH) | Neutral red (changes from colorless to pink at low pH) |\n| *E. coli* appearance | Dark purple-black with **metallic green sheen** | Flat, dry, dark pink with bile precipitate halo |\n| *Klebsiella* appearance | Large, dark pink-brown, very mucoid | Large, dark pink, mucoid |\n| Non-fermenters | Colorless\u002Ftransparent | Colorless\u002Fpale |\n| Gram-positive inhibition | Yes (dyes) | Yes (crystal violet + bile) |\n| Fastidious GNR inhibition | More inhibitory | Less inhibitory (no crystal violet) |\n| Sucrose fermenters | Not detected on Levine EMB; detected on the original formulation | Not detected |\n| Water quality testing | Preferred, *E. coli* metallic sheen = fecal coliform | Used but metallic sheen not produced |\n| Historical use | Fecal coliform differentiation | Enteric pathogen isolation |\n| FDA-BAM approved | Yes, for *E. coli* in food\u002Fwater | Yes |\n\n**The key practical difference:** MacConkey is more commonly used in clinical laboratories for routine stool and urine cultures because its neutral red indicator is more stable and the pink\u002Fcolorless distinction is simpler to read.\n\nEMB is essential in water microbiology where the metallic green sheen provides definitive identification of *E. coli* as a fecal indicator, and in settings where distinguishing *E. coli* from *Klebsiella* colony morphology is required.\n\n**When to use EMB over MacConkey:**\n\n- When the metallic green sheen of *E. coli* is specifically needed for presumptive fecal coliform identification (water testing, food microbiology)\n\n**When to use MacConkey over EMB:**\n\n- Routine clinical specimen plating: MacConkey is less inhibitory for some fastidious gram-negatives\n- When observing swarming pattern of *Proteus*: bile salts in MacConkey better inhibit swarming\n\n**In clinical practice:** Both are often inoculated simultaneously from the same specimen to maximize information: MacConkey for Enterobacteriaceae identification and *Proteus* assessment; EMB for presumptive *E. coli* confirmation by metallic sheen.\n\n→ [MacConkey Agar: Composition, Preparation, Uses and Colony Characteristics](https:\u002F\u002Fmicrobeonline.com\u002Fmacconkey-agar-mac-composition-preparation-uses-and-colony-characteristics\u002F)\n\n## How to Remember\n\n**EMB = dye-based selection and differentiation**\n\nBoth eosin Y and methylene blue are dyes that:\n\n- **Inhibit Gram-positives** (dye uptake disrupts cell membrane function)\n- **Act as pH indicators** (combine at acid pH → dark purple precipitate → metallic green sheen when dense)\n\n**The sheen is physics, not chemistry.** Remind yourself: the metallic green is light reflecting off a dense dark layer, not a green pigment. This is why it only appears in reflected light and disappears under transmitted light.\n\n**Three colony types, three clinical meanings:**\n\n| Colony on EMB | What it means | What to do next |\n| --- | --- | --- |\n| Metallic green sheen | Vigorous LF, probably *E. coli* | Confirm with IMViC, TSI, or [MALDI-TOF](https:\u002F\u002Fmicrobeonline.com\u002Fmaldi-tof-ms-principle-applications-microbiology\u002F) |\n| Mucoid, dark center, no sheen | Moderate LF, probably *Klebsiella\u002FEnterobacter* | Confirm with urease, indole, Voges-Proskauer |\n| Colorless | Non-fermenter, possibly *Salmonella* or *Shigella* | Pick for TSI + serology immediately |\n\n**EMB vs MacConkey:** **EMB is for when you need to identify *E. coli* specifically (water testing, fecal coliform confirmation)**. MacConkey is for when you need a general enteric screen. In clinical practice, use MacConkey; in water microbiology, use EMB.\n\n## Where Students Get Confused\n\n- **The green sheen is physics, not a green pigment.** The metallic green is light reflecting off a dense layer of precipitated dye, like the sheen on a soap bubble or oil film. It appears only in reflected light (light shining down onto the plate) and can vanish under transmitted light, where the same colony looks simply dark. Reading only in transmitted light is the most common way the sheen is missed.\n- **Dark colony does not always mean sheen-positive.** *Klebsiella* and *Enterobacter* ferment lactose enough to make dark pink-brown colonies, but not vigorously enough for the dense dye layer that produces the sheen. Dark and mucoid without sheen points to *Klebsiella*; dark with a metallic green sheen points to *E. coli*.\n- **Colorless does not distinguish Salmonella from Shigella.** Both are non-fermenters and both are colorless on EMB. EMB narrows them to the non-fermenter group but cannot separate them. Pick colorless colonies for TSI and serology.\n- **Late fermenters can read colorless at 24 hours.** *Citrobacter freundii* and *Shigella sonnei* may look pale at 24 hours and darken by 48 hours. Confirm a non-fermenter appearance with a 48-hour read before reporting it.\n- **A sheen on the original EMB is not the same as on Levine EMB.** On the older sucrose-containing formulation, a sucrose fermenter could also produce a sheen, which is a false positive for *E. coli*. Levine EMB (lactose only) is used precisely to avoid this. Know which formulation your laboratory uses.\n\n**References and further readings**\n\n- Tille PM. Bailey & Scott's Diagnostic Microbiology. 15th ed. St. Louis: Elsevier; 2022.\n- Leber AL, editor. Clinical Microbiology Procedures Handbook. 4th ed. Washington, DC: ASM Press; 2016.\n- Procop GW, Koneman EW. Koneman's Color Atlas and Textbook of Diagnostic Microbiology. 7th ed. Wolters Kluwer; 2017.\n- US Food and Drug Administration. Bacteriological Analytical Manual (BAM). FDA; 2023.\n- Holt-Harris JE, Teague O. A new culture medium for the isolation of Bacillus typhosus from stools. J Infect Dis. 1916;18(5):596–600.\n- Cheesbrough M. District Laboratory Practice in Tropical Countries, Part 2. 2nd ed. Cambridge University Press; 2006.",[50,53,56,59,62,65,68],{"question":51,"answer":52},"\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":54,"answer":55},"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":57,"answer":58},"\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":60,"answer":61},"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":63,"answer":64},"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":66,"answer":67},"\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":69,"answer":70},"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>",[72],"bacterial-culture-media",[74,94,121,157,183,207,240,266],{"slug":75,"title":76,"description":77,"seoTitle":42,"seoDescription":42,"author":78,"createdDate":79,"lastUpdatedDate":45,"draft":46,"category":80,"image":42,"faq":81,"tags":91},"analysis-of-water-membrane-filtration-technique","Membrane Filtration Technique: Principle, Procedure, and Bacteriological Analysis of Water","Membrane filtration concentrates bacteria from large water volumes onto a 0.45 µm filter for direct colony counting. Learn the principle, step-by-step procedure, mEndo vs mFC agar colony interpretation, CFU\u002F100 mL calculation, and how membrane filtration compares to MPN and plate count methods.","Nisha Rijal","2019-09-10","general-microbiology",[82,85,88],{"question":83,"answer":84},"Why is membrane filtration preferred over MPN for most drinking water quality testing?","\u003Cp>Membrane filtration offers three practical advantages over MPN for routine drinking water testing. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>First, it can process 100 mL or more per membrane, compared to the 15–55 mL total volume used across all MPN tubes. This larger sample volume gives much greater sensitivity for detecting low counts, which is essential when regulatory limits are expressed per 100 mL. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>Second, it gives direct colony counts rather than statistical estimates; the precision of a direct count is higher than the wide confidence intervals of an MPN estimate, particularly at low organism concentrations. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>Third, it gives presumptive results within 18–24 hours (one incubation period), whereas the MPN three-step process requires 48–72 hours. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>The primary limitation of membrane filtration is that it cannot be used for turbid, sediment-laden, or viscous water samples because suspended particles block membrane pores before adequate volume is filtered. For turbid samples, MPN remains the appropriate method because it works on any liquid sample regardless of turbidity.\u003C\u002Fp>",{"question":86,"answer":87},"\u003Cp>Why does mEndo agar produce a metallic green sheen on \u003Cem>E. coli \u003C\u002Fem>colonies but not on other organisms?\u003C\u002Fp>","\u003Cp>The metallic green sheen on\u003Cem> E. coli \u003C\u002Fem>colonies on mEndo agar (and EMB agar) is produced by the precipitation of aldehyde-reduced basic fuchsin onto the surface of colonies that have rapidly and vigorously fermented lactose. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>\u003Cem>E. coli\u003C\u002Fem> is a strong, rapid lactose fermenter. It produces large amounts of acid quickly from lactose metabolism. This acid production causes the basic fuchsin indicator in the medium to precipitate as a metallic layer on and around the colony surface. The metallic sheen is not a pigment produced by \u003Cem>E. coli\u003C\u002Fem> itself but a chemical precipitation reaction that occurs only when acid production is rapid and concentrated enough to overwhelm the buffering capacity of the medium. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>Non-E. coli coliforms that ferment lactose more slowly (such as \u003Cem>Enterobacter\u003C\u002Fem> species) produce pink-metallic colonies rather than the brilliant metallic green sheen characteristic of \u003Cem>E. coli\u003C\u002Fem>. Non-fermenters produce colorless to pale colonies with no sheen. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>This differential reaction allows presumptive identification of \u003Cem>E. coli\u003C\u002Fem> directly from the membrane filtration plate without further testing.\u003C\u002Fp>",{"question":89,"answer":90},"What is the mFC agar incubation temperature and why is it different from standard incubation?","\u003Cp>mFC (membrane fecal coliform) agar is incubated at 44.5°C ± 0.2°C, a temperature significantly higher than the standard 35–37°C used for total coliform detection on mEndo agar. This elevated temperature is the basis of the fecal coliform selectivity: organisms adapted to the warm intestinal environment of warm-blooded animals (37°C body temperature) can tolerate this elevated incubation temperature and continue to ferment lactose, producing blue colonies on mFC agar. Non-fecal coliforms and most environmental organisms, which are adapted to cooler ambient temperatures, are inhibited or fail to ferment lactose at 44.5°C. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>The tight temperature tolerance (±0.2°C) means that incubation in a water bath is strongly preferred over an air incubator, which has less precise temperature control. Even a 0.5°C deviation from 44.5°C can significantly affect sensitivity and specificity: too low a temperature allows false-positive growth of non-fecal organisms; too high suppresses even true fecal coliforms. This precision requirement is why water bath incubation is specified in standard methods for fecal coliform detection.\u003C\u002Fp>",[92,93],"bacterial-enumeration","water-quality-testing",{"slug":95,"title":96,"description":97,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":98,"lastUpdatedDate":99,"draft":46,"category":100,"image":42,"faq":101,"tags":120},"enterobacteriaceae","Enterobacteriaceae: How to Identify and Tell Them Apart","A working guide to the Enterobacteriaceae: which genera matter, how lactose fermentation and biochemical tests separate them, and how to reason from a MacConkey plate to a genus.","2013-10-01","2026-08-18","bacteriology",[102,105,108,111,114,117],{"question":103,"answer":104},"\u003Cp>What is the single fastest test to know a Gram-negative rod belongs to the Enterobacteriaceae?\u003C\u002Fp>","\u003Cp>The oxidase test. Members of this family are oxidase-negative. If a Gram-negative rod is oxidase-positive, it is not in this family, and you should think of organisms such as \u003Cem>Pseudomonas\u003C\u002Fem> or \u003Cem>Vibrio\u003C\u002Fem> instead.\u003C\u002Fp>",{"question":106,"answer":107},"\u003Cp>Why are Salmonella and Shigella pale on MacConkey agar?\u003C\u002Fp>","\u003Cp>Because they do not ferment lactose. MacConkey agar turns pink only when an organism ferments lactose and lowers the pH. \u003Cem>Salmonella\u003C\u002Fem> and \u003Cem>Shigella\u003C\u002Fem> are non-lactose fermenters, so their colonies stay colorless. This is why a pale colony in a diarrheal stool is the one worth investigating.\u003C\u002Fp>",{"question":109,"answer":110},"\u003Cp>Is Enterobacteriaceae the same as Enterobacterales?\u003C\u002Fp>","\u003Cp>Not exactly. In 2016 the old family was reorganized into a larger order called Enterobacterales, and some genera were moved into separate families. In everyday clinical and exam use, the term Enterobacteriaceae is still used broadly for this whole group of enteric Gram-negative rods.\u003C\u002Fp>",{"question":112,"answer":113},"\u003Cp>What does IMViC stand for and why is it useful?\u003C\u002Fp>","\u003Cp>IMViC stands for Indole, Methyl red, Voges-Proskauer, and Citrate. These four tests together separate the common genera. The classic contrast is \u003Cem>E. coli\u003C\u002Fem> (+ + − −) versus \u003Cem>Klebsiella\u003C\u002Fem> and \u003Cem>Enterobacter\u003C\u002Fem> (− − + +).\u003C\u002Fp>",{"question":115,"answer":116},"\u003Cp>Which Enterobacteriaceae are the main antibiotic-resistance concerns?\u003C\u002Fp>","\u003Cp>Three groups: organisms with inducible AmpC beta-lactamase (such as \u003Cem>Enterobacter\u003C\u002Fem>, \u003Cem>Serratia\u003C\u002Fem>, \u003Cem>Citrobacter freundii\u003C\u002Fem>, \u003Cem>Klebsiella aerogenes\u003C\u002Fem>), ESBL-producers (common in \u003Cem>E. coli\u003C\u002Fem> and \u003Cem>Klebsiella\u003C\u002Fem>), and carbapenem-resistant Enterobacteriaceae (CRE), where treatment options become very limited.\u003C\u002Fp>",{"question":118,"answer":119},"\u003Cp>What is the Vi antigen?\u003C\u002Fp>","\u003Cp>It is a special capsular antigen of \u003Cem>Salmonella\u003C\u002Fem> Typhi. \"Vi\" stands for virulence. It can cover the O antigen on fresh isolates, which is why an O-antigen agglutination test may read negative until the culture is heated.\u003C\u002Fp>",[95],{"slug":122,"title":123,"description":124,"seoTitle":123,"seoDescription":125,"author":78,"createdDate":126,"lastUpdatedDate":127,"draft":46,"category":128,"image":42,"faq":129,"tags":154},"autoclave-principle-procedure-types-and-uses","Autoclave Sterilization: Cycles, Validation, Uses, and Failures","How steam sterilization actually works, the cycles and pressures for each load type, how to validate a run with biological and chemical indicators, what cannot be autoclaved, and the practical reasons cycles fail (trapped air, wet packs, and false-passing tape).","Understand autoclave steam sterilization cycles, loading, validation indicators, common uses, and the practical causes of wet packs and failed runs.","2019-10-03","2026-07-29","lab-equipment",[130,133,136,139,142,145,148,151],{"question":131,"answer":132},"What is the standard autoclave temperature, pressure, and time?","121°C at 15 psi for 15-20 minutes minimum. Holding time measured from when all materials in the load reach 121°C — not just the chamber gauge.",{"question":134,"answer":135},"Why is it temperature not pressure that sterilizes?","Pressure only raises boiling point to generate 121°C steam. High temperature denatures proteins and destroys nucleic acids. Steam at 100°C (atmospheric) cannot kill bacterial endospores.",{"question":137,"answer":138},"Why must all air be removed?","Air pockets prevent steam contact. Air-steam mixtures at 15 psi reach only ~112°C — too low. Complete air removal ensures 121°C throughout the entire load.",{"question":140,"answer":141},"What biological indicator tests autoclave effectiveness?","Geobacillus stearothermophilus spores — D-value 1.5-2.5 min at 121°C. CDC recommends weekly testing. For dry heat (hot air oven): Bacillus atrophaeus spores.",{"question":143,"answer":144},"Can you autoclave liquids in sealed containers?","Never — pressure differential when cycle ends can cause explosive rupture. Always loosen caps before autoclaving.",{"question":146,"answer":147},"Why are oils and powders not sterilized by autoclave?","Oils repel steam; powders trap air — both prevent steam penetration. Use dry heat sterilization (160-170°C) where conduction-based heat penetration is independent of steam.",{"question":149,"answer":150},"What is the difference between gravity displacement and pre-vacuum autoclave?","Gravity: steam slowly pushes air out — may leave air pockets. Pre-vacuum: pump actively removes air first ensuring complete steam penetration. Required for wrapped surgical packs.",{"question":152,"answer":153},"What cycle is recommended for prion-contaminated materials?","134°C for 18 minutes (pre-vacuum) OR NaOH\u002Fhypochlorite treatment + 134°C for 1 hour. Standard 121°C cycles do not inactivate prions. Single-use instruments preferred for CJD\u002FvCJD cases.",[155,156],"sterilization-disinfection","laboratory-heating-equipment",{"slug":158,"title":159,"description":160,"seoTitle":161,"seoDescription":42,"author":162,"createdDate":163,"lastUpdatedDate":164,"draft":46,"category":128,"image":42,"faq":165,"tags":181},"petri-dish-types-uses-and-automated-petri-dish-filler","Petri Dish: Types, Uses, Why the Lid Doesn't Seal, and Why Plates Are Incubated Upside Down","Petri dish types and uses, why its lid rests loosely instead of sealing, why culture plates are incubated upside down, and how to pour agar at the right temperature. A guide for microbiology students.","Petri Dish: Types, Uses, and How to Pour and Incubate Plates Correctly","Sushmita Baniya","2022-10-12","2026-07-30",[166,169,172,175,178],{"question":167,"answer":168},"\u003Cp>Why is a Petri dish lid not sealed?\u003C\u002Fp>","\u003Cp>The lid rests loosely over the base, larger than it, leaving a small gap. This lets growing microorganisms exchange gases with the air, which aerobic bacteria need, while the overhanging rim and still air in the gap keep airborne contaminants from falling onto the media. A sealed dish would suffocate the culture.\u003C\u002Fp>",{"question":170,"answer":171},"\u003Cp>Why are Petri dishes incubated upside down?\u003C\u002Fp>","\u003Cp>Plates are incubated inverted, with the lid on the bottom, so that water evaporating from the warm agar condenses on the lid instead of dripping onto the colonies. Incubating right-side up lets condensation fall onto the media, smearing the colonies and risking contamination.\u003C\u002Fp>",{"question":173,"answer":174},"\u003Cp>At what temperature should molten agar be poured into a Petri dish?\u003C\u002Fp>","\u003Cp>Agar is poured at about 45 to 50°C, tempered in a water bath. This is cool enough not to destroy heat-sensitive additives such as blood, but still liquid enough to pour evenly. It then solidifies as it cools below about 40°C.\u003C\u002Fp>",{"question":176,"answer":177},"\u003Cp>Why is a Petri dish labeled on the bottom, not the lid?\u003C\u002Fp>","\u003Cp>Lids are interchangeable and easily swapped between plates during handling. Labeling the base keeps each culture tied to its correct sample and prevents mix-ups that could cause false reporting.\u003C\u002Fp>",{"question":179,"answer":180},"\u003Cp>What is the difference between a glass and a plastic Petri dish?\u003C\u002Fp>","\u003Cp>Glass dishes are reusable and must be sterilized between uses, usually by dry heat at 160°C or by autoclaving. Plastic dishes come pre-sterilized from the manufacturer and are discarded after a single use.\u003C\u002Fp>",[182],"laboratory-glassware",{"slug":184,"title":185,"description":186,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":187,"lastUpdatedDate":188,"draft":46,"category":128,"image":42,"faq":189,"tags":205},"laboratory-refrigerator-temperature-and-storage","Laboratory Refrigerator: Temperature, What to Store at Each, and Storage Rules","Laboratory refrigerator temperatures explained, which reagents, sera, vaccines, and blood products belong at 2-8 degrees C, why freezing destroys some of them, and the storage rules that keep samples usable. A practical guide for lab science students.","2026-07-28","2026-08-12",[190,193,196,199,202],{"question":191,"answer":192},"What temperature is a laboratory refrigerator set to?","A laboratory refrigerator is kept at 2–8°C, with about 4°C as the usual set point. This range slows chemical reactions, enzyme activity, and microbial growth while staying above freezing, which protects reagents, sera, vaccines, and blood products that ice crystals would damage.",{"question":194,"answer":195},"Why are some reagents and vaccines refrigerated instead of frozen?","Freezing forms ice crystals that denature proteins and rupture cells, which destroys many control sera, antibodies, and vaccines. For these items, 2–8°C preserves activity while freezing would ruin them, so colder is not automatically better.",{"question":197,"answer":198},"Why are platelets not stored in the refrigerator?","Platelets are stored at 20–24°C (room temperature) with continuous gentle agitation. Refrigeration damages platelet function and stillness causes them to clump, so unlike red cells and plasma, platelets are never refrigerated.",{"question":200,"answer":201},"Why should nothing sensitive be stored in the refrigerator door?","The door is the warmest and most temperature-variable part of the refrigerator, because it warms every time the fridge is opened. Sensitive items such as controls, sera, vaccines, and blood should be kept on the internal shelves where the temperature is stable.",{"question":203,"answer":204},"What is the difference between a laboratory refrigerator and a blood bank refrigerator?","A blood bank refrigerator is a specialized laboratory refrigerator held at 2–6°C with a tighter temperature tolerance, a continuous temperature log, and an audible alarm. The stricter monitoring exists because a temperature error can make blood unsafe to transfuse.",[206],"laboratory-storage-and-preservation",{"slug":208,"title":209,"description":210,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":211,"lastUpdatedDate":212,"draft":46,"category":128,"image":42,"faq":213,"tags":238},"types-of-swabs","Types of Swabs in Microbiology: Materials, Design, and Which Swab to Use","Compare cotton, calcium alginate, Dacron, rayon, and nylon flocked swabs, and see which swab and shaft to use for each specimen type, from throat and wound to pertussis and GC culture.","2022-11-08","2026-07-23",[214,217,220,223,226,229,232,235],{"question":215,"answer":216},"Which swab should I use for a nasopharyngeal specimen?","A nylon flocked or Dacron swab on a flexible plastic shaft, ideally a minitip for nasopharyngeal use. Cotton, calcium alginate, and wooden shafts should all be avoided, because they either inhibit PCR, inactivate viruses, or risk injury.",{"question":218,"answer":219},"Why can't I use cotton swabs for microbiology?","Cotton fails in two independent ways. Fatty acids in the fiber are directly toxic to fastidious organisms such as Bordetella pertussis and Neisseria gonorrhoeae, and residues from cotton inhibit PCR amplification. So a cotton swab can give a false negative either by killing the organism or by blocking its detection.",{"question":221,"answer":222},"Are calcium alginate swabs still used?","They are largely obsolete in diagnostic microbiology. Calcium alginate is toxic to tissue culture, inactivates certain viruses including herpes simplex virus, is toxic to gonococci and mycoplasmas, and interferes with PCR and fluorescent antibody tests. Older textbooks recommending it for nasopharyngeal collection are out of date.",{"question":224,"answer":225},"What is a flocked swab and why is it better?","A flocked swab has short nylon fibers standing perpendicular to the applicator with no internal core, rather than fiber wound around a core. Sample stays near the surface and elutes almost completely into liquid medium. Around 90 percent of the collected sample becomes available for testing, compared with roughly 10 percent from a traditional fiber swab, and one collection can supply several tests.",{"question":227,"answer":228},"Is a flocked swab always the best choice?","No. For nucleic acid testing, nylon flocked swabs give clearly better DNA yield, more than three and a half times that of rayon. But for antigen-based point-of-care tests, which depend on protein recovery, rayon and Dacron actually perform best and cost less. The best swab depends on the assay.",{"question":230,"answer":231},"Why are wooden shafts not recommended?","Wood is toxic to several organisms including Chlamydia trachomatis and various viruses, it releases substances that inhibit PCR, and it can splinter, which is a genuine injury risk in nasopharyngeal collection. Plastic shafts are recommended for all diagnostic collection.",{"question":233,"answer":234},"Which transport medium goes with which swab?","For general bacteriology use Amies medium, with charcoal for fastidious organisms. For enteric pathogens use Cary-Blair. For viral specimens use viral or universal transport medium, since bacterial transport media are unsuitable for viruses. Liquid-based systems such as eSwab combine a flocked swab with liquid Amies for multi-test workflows.",{"question":236,"answer":237},"Is a swab as good as a tissue sample or aspirate?","No. Where tissue, pus, or a needle aspirate can be obtained, it is almost always the better specimen, because it carries more organisms, provides enough material for multiple tests, and gives better anaerobe recovery. Swabs are appropriate where the site suits them, such as the throat or nasopharynx, or where nothing better can be obtained.",[239],"specimen-collection-transport",{"slug":241,"title":242,"description":243,"seoTitle":42,"seoDescription":42,"author":162,"createdDate":244,"lastUpdatedDate":245,"draft":46,"category":128,"image":42,"faq":246,"tags":265},"inoculating-loop-types-and-uses","Inoculating Loop: Types, Parts, Uses, and Sterilisation in Microbiology","\u003Cp>The inoculating loop is the primary instrument for transferring and streaking bacteria in microbiology. Learn its types (nichrome, platinum, disposable, calibrated), how to sterilize and cool it correctly, clinical uses including semi-quantitative urine culture, and common errors.\u003C\u002Fp>","2022-10-18","2026-08-14",[247,250,253,256,259,262],{"question":248,"answer":249},"What is the difference between an inoculating loop and an inoculating needle?","\u003Cp>An inoculating loop has a circular wire end and is used for surface transfers: streak plates, smear preparation, and broth inoculation. An inoculating needle has a straight wire end and is used for depth inoculation: stabbing semi-solid media such as SIM, TSI butt, gelatin, and motility media. The rule is: loop for surface, needle for depth.\u003C\u002Fp>",{"question":251,"answer":252},"Why must the inoculating loop be cooled before touching the specimen or agar?","\u003Cp>After flaming to red heat (above 800°C), the loop is hot enough to kill bacteria on contact and melt agar on touch. Cooling for 15–30 seconds allows the wire to reach a safe temperature. You can test the loop by briefly touching the agar edge away from any growth, if the agar crackles or the loop hisses, wait longer before proceeding.\u003C\u002Fp>",{"question":254,"answer":255},"Why are disposable plastic loops preferred for handling infectious specimens?","\u003Cp>Flaming a metal loop that carries infectious material generates aerosols, fine droplets containing viable organisms that become airborne. Disposable plastic loops are pre-sterilized and discarded after a single use, eliminating both the aerosol risk from flaming and the need for a Bunsen burner. They are the preferred choice in BSL-2 and BSL-3 work and in anaerobic chambers where open flames are prohibited.\u003C\u002Fp>",{"question":257,"answer":258},"What is a calibrated loop and what is it used for?","\u003Cp>A calibrated loop delivers a precise, defined volume of liquid  (either 1 µL or 10 µL) rather than an approximate loopful. In clinical microbiology, calibrated loops are used for semi-quantitative urine culture: the loop delivers a known volume of urine onto a CLED plate, colonies are counted after 24 hours of incubation, and the count is multiplied by the dilution factor to estimate CFU\u002FmL. Significant bacteriuria is defined as ≥10⁵ CFU\u002FmL. For full details on the urine culture procedure, see the Laboratory Diagnosis of UTI article.\u003C\u002Fp>",{"question":260,"answer":261},"What is the most common error when using an inoculating loop for a streak plate?","The most common error is re-entering a previous streak area without first re-sterilising the loop. This carries organisms back into an area already diluted, destroying the dilution gradient that produces isolated colonies. Each new quadrant must be entered only from the last few streaks of the previous area, and the loop must be flamed and cooled between quadrants.",{"question":263,"answer":264},"Why is nichrome wire preferred over platinum for routine laboratory loops?","\u003Cp>Nichrome wire (a nickel-chromium alloy) heats and cools rapidly, is resistant to corrosion, and costs significantly less than platinum, typically 10 to 20 times cheaper. It is durable enough for repeated flaming in routine bacteriology. Platinum wire is reserved for specialized applications where its superior acid resistance or longer working life under extreme conditions justifies the higher cost.\u003C\u002Fp>",[],{"slug":267,"title":268,"description":269,"seoTitle":270,"seoDescription":271,"author":78,"createdDate":272,"lastUpdatedDate":45,"draft":46,"category":80,"image":42,"faq":273,"tags":283},"probable-number-mpn-test-principle-procedure-results","Most Probable Number (MPN) Test: Principle, Procedure, MPN Table, and Results","The MPN test estimates bacterial concentration using statistical probability across serial dilution tube patterns. Learn its three-step procedure (presumptive, confirmatory, completed), how to read the MPN table, worked examples, and when to use MPN over plate counts.","MPN Test: Procedure, Tables, Calculation, and Result Interpretation","Work through presumptive, confirmed, and completed MPN testing, read probability tables, calculate results, and understand when the estimate is appropriate.","2017-06-11",[274,277,280],{"question":275,"answer":276},"Why is the MPN test performed in three steps (presumptive, confirmatory, completed) rather than relying on the initial gas production result?","\u003Cp>The presumptive test detects all organisms capable of fermenting lactose with acid and gas production at 37°C within 48 hours. This group includes not just coliforms but also some non-coliform organisms. Certain \u003Cem>Aeromonas\u003C\u002Fem> species, \u003Cem>Clostridium\u003C\u002Fem> species, and occasional yeasts also produce acid and gas from lactose but are not members of the coliform group.\u003C\u002Fp>\u003Cp>Relying on the presumptive test alone would overestimate the coliform count by including these non-coliform false positives. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>The confirmatory test (subculture to brilliant green lactose bile broth or BGLB) specifically suppresses non-coliform gram-negative bacteria and most gram-positive organisms, while confirming coliforms by their ability to survive the selective agents and continue fermenting lactose with gas. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>The completed test adds microscopic examination to confirm the Gram-negative non-spore-forming bacillus morphology. Each step progressively narrows the candidates to confirmed coliforms. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>In most water quality laboratories, the presumptive and confirmatory steps are used routinely, with the completed test reserved for reference or regulatory purposes.\u003C\u002Fp>",{"question":278,"answer":279},"What is the clinical significance of detecting faecal coliforms versus total coliforms in water testing?","\u003Cp>Total coliforms include organisms from several genera (\u003Cem>Escherichia, Klebsiella, Enterobacter, Citrobacter, Serratia\u003C\u002Fem>) some of which occur naturally in soil and vegetation environments without indicating recent fecal contamination. The presence of total coliforms in water indicates a failure of water treatment or distribution system integrity, but does not specifically confirm fecal contamination. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>Fecal coliforms (thermotolerant coliforms, primarily \u003Cem>E. coli\u003C\u002Fem>) are specifically adapted to the warm, nutrient-rich intestinal environment of warm-blooded animals and are shed exclusively in feces. Their detection at 44.5°C in the MPN test confirms recent fecal contamination of the water supply and therefore the potential presence of enteric pathogens including \u003Cem>Salmonella, Shigella, Vibrio cholerae,\u003C\u002Fem> hepatitis A virus, and rotavirus. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>WHO drinking water guidelines specify zero tolerance for \u003Cem>E. coli\u003C\u002Fem> or thermotolerant coliforms in treated piped water precisely because their presence is a reliable proxy for these pathogenic organisms even when the pathogens themselves are undetectable by routine testing.\u003C\u002Fp>",{"question":281,"answer":282},"\u003Cp>Why is acid alone not enough for a positive presumptive tube, why does gas matter?\u003C\u002Fp>","\u003Cp>Many organisms can drop the pH of a lactose broth by producing acid, but only a subset of them release gas (CO₂ and H₂) during lactose fermentation. Coliforms are defined, in this test, by their ability to ferment lactose \u003Cstrong>with gas production\u003C\u002Fstrong>. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>Scoring gas (the bubble in the Durham tube) as the endpoint therefore screens out a large number of acid-only fermenters that are not coliforms, which is why the Durham tube, not the color change alone, is what you read to call a presumptive tube positive.\u003C\u002Fp>",[92,93],{"enabled":285,"threads":286,"total":287},true,[],0,[289,295,302,308,314,319,325,330,336,339,345],{"slug":290,"name":43,"description":291,"image":292,"body":293,"postCount":294},"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.*",477,{"slug":296,"name":297,"description":298,"image":299,"body":300,"postCount":301},"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.",78,{"slug":303,"name":162,"description":304,"image":305,"body":306,"postCount":307},"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":309,"name":310,"description":304,"image":311,"body":312,"postCount":313},"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":315,"name":316,"description":304,"image":42,"body":317,"postCount":318},"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":320,"name":321,"description":322,"image":42,"body":323,"postCount":324},"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":326,"name":327,"description":328,"image":42,"body":42,"postCount":329},"guest-author","Guest Author","Guest Author \u002F Contributor",1,{"slug":331,"name":332,"description":304,"image":333,"body":334,"postCount":335},"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":337,"name":338,"description":328,"image":42,"body":42,"postCount":329},"dr-poonam-acharya","Dr. Poonam Acharya",{"slug":340,"name":78,"description":341,"image":342,"body":343,"postCount":344},"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":346,"name":347,"description":348,"image":349,"body":350,"postCount":329},"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.",[352,359,365,370,375,380,384,388,391,396,400,405,409,413,417,421,425,429,434,439,443,447,451,456,460,464,468,472,477,482,486,490,494,498,502,506,509,513,517,521,525,529,533,537,541,545,549,552,556,559,563,567,571,575,579,583,587,591,595,599,603,607,611,615,619,623,627,631,634,638,641,644,647,650,653,656,659,662,665],{"slug":353,"name":354,"description":355,"image":356,"body":357,"postCount":358},"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":360,"name":361,"description":362,"image":42,"body":363,"postCount":364},"microscopy","Microscopy","Microscope types, components, and microscopy techniques","These are list of blog posts related to microscopy. ",12,{"slug":366,"name":367,"description":368,"image":42,"body":42,"postCount":369},"gram-positive-cocci","Gram-Positive Cocci","Staphylococcus, Streptococcus, Enterococcus, Micrococcus — organisms, diseases, and identification tests",11,{"slug":371,"name":372,"description":373,"image":42,"body":42,"postCount":374},"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":376,"name":377,"description":378,"image":42,"body":42,"postCount":379},"gram-positive-rods","Gram-Positive Rods","Bacillus, Clostridium, Listeria, Corynebacterium, Actinomyces and related organisms",8,{"slug":381,"name":382,"description":383,"image":42,"body":42,"postCount":369},"mycobacteria","Mycobacteria","Mycobacterium tuberculosis, leprosy, atypical mycobacteria, and acid-fast organism diagnosis",{"slug":385,"name":386,"description":387,"image":42,"body":42,"postCount":369},"anaerobic-bacteriology","Anaerobic Bacteriology","Anaerobic organisms, anaerobic culture methods, and anaerobic infection diagnosis",{"slug":95,"name":389,"description":390,"image":42,"body":42,"postCount":364},"Enterobacteriaceae","Identification, differentiation, and clinical significance of Enterobacteriaceae family members",{"slug":392,"name":393,"description":394,"image":42,"body":42,"postCount":395},"spirochetes","Spirochetes","Treponema, Leptospira, Borrelia and spirochetal infections",7,{"slug":397,"name":398,"description":399,"image":42,"body":42,"postCount":335},"food-microbiology","Food Microbiology","Food-borne pathogens, food safety, spoilage, and preservation",{"slug":401,"name":402,"description":403,"image":42,"body":42,"postCount":404},"antimicrobial-susceptibility-testing","Antimicrobial Susceptibility Testing","Methods for testing antibiotic susceptibility in clinical microbiology",21,{"slug":406,"name":407,"description":408,"image":42,"body":42,"postCount":324},"antimicrobials-moa-amr","Antimicrobials (MOA & AMR)","Mechanisms, detection, and clinical significance of antimicrobial resistance",{"slug":155,"name":410,"description":411,"image":42,"body":42,"postCount":412},"Sterilization and Disinfection","Methods of sterilization and disinfection in healthcare and laboratory settings",10,{"slug":239,"name":414,"description":415,"image":42,"body":42,"postCount":416},"Specimen Collection and Transport","Collection, handling, and transport of clinical specimens for microbiological testing",27,{"slug":418,"name":419,"description":420,"image":42,"body":42,"postCount":404},"bacterial-structure-physiology","Bacterial Structure and Physiology","Bacterial cell structure, growth, physiology, and environmental factors affecting growth",{"slug":422,"name":423,"description":42,"image":42,"body":424,"postCount":318},"horizontal-gene-transfer","Horizontal Gene Transfer","Articles related to **Horizontal Gene Transfer**",{"slug":426,"name":427,"description":42,"image":42,"body":428,"postCount":412},"chromatography","Chromatography","Information about chromatographic techniques.",{"slug":430,"name":431,"description":432,"image":42,"body":433,"postCount":395},"electrophoresis","Electrophoresis","Information about Electrophoresis Techniques ","Detailed information  about Electrophoresis Techniques ",{"slug":435,"name":436,"description":437,"image":42,"body":438,"postCount":318},"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":440,"name":441,"description":442,"image":42,"body":42,"postCount":318},"bacteriophage","Bacteriophage","Description about Bacteriophage.",{"slug":444,"name":445,"description":446,"image":42,"body":42,"postCount":318},"malaria","Malaria","It is the collections of articles regarding malarial disease. ",{"slug":448,"name":449,"description":450,"image":42,"body":42,"postCount":318},"anaerobic-culture-techniques","Anaerobic Culture Techniques","Posts related with Anaerobic Culture Techniques.",{"slug":452,"name":453,"description":454,"image":42,"body":42,"postCount":455},"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":457,"name":458,"description":459,"image":42,"body":42,"postCount":395},"biosafety-levels","Biosafety levels ","Articles related to Biosafety Levels",{"slug":461,"name":462,"description":463,"image":42,"body":42,"postCount":374},"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":465,"name":466,"description":467,"image":42,"body":42,"postCount":318},"pipette","Pipette","Posts related with Pipette. ",{"slug":469,"name":470,"description":471,"image":42,"body":42,"postCount":379},"bacteriology-mcqs","Bacteriology MCQs","This sections lists MCQs in Bacteriology.",{"slug":473,"name":474,"description":475,"image":42,"body":42,"postCount":476},"parasitology-mcqs","Parasitology MCQs","This section lists MCQs in Parasitology.",2,{"slug":478,"name":479,"description":480,"image":42,"body":42,"postCount":481},"virology-mcqs","Virology MCQs","This is the collections of Multiple Choice Questions in Virology.",4,{"slug":483,"name":484,"description":485,"image":42,"body":42,"postCount":374},"mcqs-in-microbiology","MCQs in Microbiology","This section lists the collections of Multiple Choice Questions in General Microbiology Topics. ",{"slug":487,"name":488,"description":489,"image":42,"body":42,"postCount":379},"immunology-mcqs","Immunology MCQs","In this section; we are posting collections of Multiple Choice Questions about Immunology. ",{"slug":491,"name":492,"description":493,"image":42,"body":42,"postCount":324},"microbial-curiosities","Microbial Curiosities","In this clusters, we are posting interesting and unique information about Microorganisms. ",{"slug":72,"name":495,"description":496,"image":42,"body":42,"postCount":497},"Bacterial Culture Media","Posts related to Bacterial Culture Media. ",23,{"slug":499,"name":500,"description":501,"image":42,"body":42,"postCount":318},"fungal-culture-media","Fungal Culture Media","Posts related to Fungal Culture Media.",{"slug":503,"name":504,"description":505,"image":42,"body":42,"postCount":374},"motility-test","Motility Test","This lists the procedure regarding various tests methods for bacterial motility.",{"slug":92,"name":507,"description":508,"image":42,"body":42,"postCount":412},"Bacterial enumeration","These posts are related to isolation and enumeration of bacteria. ",{"slug":510,"name":511,"description":512,"image":42,"body":42,"postCount":476},"gram-positive-coccobacillus","Gram-positive coccobacillus","List of Gram Positive Coccobacilli",{"slug":514,"name":515,"description":516,"image":42,"body":42,"postCount":481},"dimorphic-fungi","Dimorphic Fungi","This is about various dimorphic fungi. ",{"slug":518,"name":519,"description":520,"image":42,"body":42,"postCount":395},"bacterial-classification","Bacterial Classification","These posts are related with various approaches used for the classification of Bacteria. ",{"slug":522,"name":523,"description":524,"image":42,"body":42,"postCount":374},"immunofluorescence","Immunofluorescence ","Various Tests related to Immunofluorescence ",{"slug":526,"name":527,"description":528,"image":42,"body":42,"postCount":324},"antibody-mediated-immunity","Antibody-mediated Immunity","This clusters links the articles that are sharing insights about Antibody-mediated immunity. ",{"slug":530,"name":531,"description":532,"image":42,"body":42,"postCount":395},"hypersensitivity","Hypersensitivity","Articles related to Hypersensitivity.",{"slug":534,"name":535,"description":42,"image":42,"body":42,"postCount":536},"haemophilus","Haemophilus",3,{"slug":538,"name":539,"description":540,"image":42,"body":42,"postCount":481},"sexually-transmitted-infections-stis","Sexually transmitted infections (STIs)","This is the clusters of infections that are transmitted sexually. ",{"slug":542,"name":543,"description":544,"image":42,"body":42,"postCount":364},"adaptive-immunity","Adaptive Immunity","Blog posts related to B Cell Immunity and T Cell Immunity.",{"slug":546,"name":547,"description":548,"image":42,"body":42,"postCount":358},"fungal-diagnostics","Fungal Diagnostics","Various methods used for the Diagnosis of Fungal Infections. ",{"slug":206,"name":550,"description":551,"image":42,"body":42,"postCount":374},"Laboratory Storage and Preservation","Articles about Laboratory Storage of Antimicrobial Disk, Test organisms and Equipment used for this process. ",{"slug":156,"name":553,"description":554,"image":42,"body":555,"postCount":318},"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":182,"name":557,"description":558,"image":42,"body":42,"postCount":324},"Laboratory Glassware","Posts about Laboratory Glassware. ",{"slug":560,"name":561,"description":562,"image":42,"body":42,"postCount":318},"helminths","Helminths","In this section, we are covering properties, life cycle, pathogenesis and laboratory diagnosis of Helminths\u002FHelminthic infestations. ",{"slug":564,"name":565,"description":566,"image":42,"body":42,"postCount":395},"protozoan-parasite","Protozoan Parasite","In this cluster, we are covering protozoan parasites. ",{"slug":568,"name":569,"description":570,"image":42,"body":42,"postCount":329},"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":572,"name":573,"description":574,"image":42,"body":42,"postCount":412},"bacterial-staining-technique","Bacterial Staining Technique","Lists of various staining techniques that are used to stain bacteria. ",{"slug":576,"name":577,"description":578,"image":42,"body":42,"postCount":404},"enzyme-tests","Enzyme Tests","\u003Cp>Various Biochemical Test that are based on enzymatic activity of the microorganisms. \u003C\u002Fp>",{"slug":580,"name":581,"description":582,"image":42,"body":42,"postCount":369},"carbohydrate-utilization","Carbohydrate Utilization","\u003Cp>Various biochemical tests which are related to Carbohydrate fermentation or Utilization\u003C\u002Fp>",{"slug":584,"name":585,"description":586,"image":42,"body":42,"postCount":374},"susceptibility-based-id","Susceptibility-based ID","\u003Cp>These are susceptibility based identification test such as optochin sensitivity, bacitracin sensitivity etc. \u003C\u002Fp>",{"slug":588,"name":589,"description":590,"image":42,"body":42,"postCount":481},"microbial-metabolism","Microbial Metabolism","\u003Cp>Tests about Microbial Metabolism. \u003C\u002Fp>",{"slug":592,"name":593,"description":594,"image":42,"body":42,"postCount":379},"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":596,"name":597,"description":598,"image":42,"body":42,"postCount":536},"atypical-pneumonia","Atypical Pneumonia","\u003Cp>Organisms responsible for Atypical Pneumonia. \u003C\u002Fp>",{"slug":600,"name":601,"description":602,"image":42,"body":42,"postCount":374},"antigen","Antigen","\u003Cp>Various articles related to Antigens.\u003C\u002Fp>",{"slug":604,"name":605,"description":606,"image":42,"body":42,"postCount":395},"innate-immunity","Innate Immunity","\u003Cp>Articles related to Innate Immunity. \u003C\u002Fp>",{"slug":608,"name":609,"description":610,"image":42,"body":42,"postCount":481},"respiratory-tract-infection","Respiratory Tract Infection","\u003Cp>In this cluster, you can see various etiological agents that causes respiratory tract infection. \u003C\u002Fp>",{"slug":612,"name":613,"description":614,"image":42,"body":42,"postCount":374},"torch-infection","TORCH Infection","\u003Cp>In this section; you can find articles related with TOCH infection. \u003C\u002Fp>",{"slug":616,"name":617,"description":618,"image":42,"body":42,"postCount":395},"microbiology-for-beginners","Microbiology for Beginners","\u003Cp>These articles are very basic articles, which will share general concepts in Microbiology. \u003C\u002Fp>",{"slug":620,"name":621,"description":622,"image":42,"body":42,"postCount":318},"dna-replication","DNA Replication","\u003Cp>Articles related to DNA and Replication of DNA. \u003C\u002Fp>",{"slug":624,"name":625,"description":626,"image":42,"body":42,"postCount":395},"genetic-code","Genetic Code","\u003Cp>Articles related to Genetic Code.\u003C\u002Fp>",{"slug":628,"name":629,"description":630,"image":42,"body":42,"postCount":374},"molecular-technique","Molecular Technique","\u003Cp>Posts related to Molecular Techniques. \u003C\u002Fp>",{"slug":632,"name":633,"description":42,"image":42,"body":42,"postCount":329},"colorimetric-assay","Colorimetric Assay ",{"slug":635,"name":636,"description":637,"image":42,"body":42,"postCount":374},"pharmaceutical-microbiology","Pharmaceutical Microbiology","\u003Cp>Various articles related to Pharmaceutical Microbiology\u003C\u002Fp>",{"slug":639,"name":640,"description":42,"image":42,"body":42,"postCount":536},"blood-and-immune-cells","Blood and Immune Cells",{"slug":642,"name":643,"description":42,"image":42,"body":42,"postCount":374},"host-pathogen-interaction","Host Pathogen Interaction",{"slug":645,"name":646,"description":42,"image":42,"body":42,"postCount":481},"blood-culture","Blood Culture",{"slug":648,"name":649,"description":42,"image":42,"body":42,"postCount":481},"environmental-microbiology","Environmental microbiology ",{"slug":651,"name":652,"description":42,"image":42,"body":42,"postCount":318},"copromicroscopic-technique","Copromicroscopic Technique",{"slug":654,"name":655,"description":42,"image":42,"body":42,"postCount":536},"quality-control","Quality Control",{"slug":657,"name":658,"description":42,"image":42,"body":42,"postCount":481},"dermatophytes","Dermatophytes",{"slug":660,"name":661,"description":42,"image":42,"body":42,"postCount":536},"viral-hemorrhagic-fevers","Viral Hemorrhagic Fevers",{"slug":663,"name":664,"description":42,"image":42,"body":42,"postCount":481},"h2s-production","H2S Production",{"slug":93,"name":666,"description":42,"image":42,"body":42,"postCount":476},"Water Quality Testing"]