[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fYJORRw_aF31z-S_03wPGPaI4UBRmIh1pctAmjE5QO14":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":157},[4,8,12,16,20,24,28],{"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},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":47},"pus-sample-collection-staining-culture","Pus Sample: Collection, Processing, Staining and Culture",null,"Acharya Tankeshwar","2019-02-07","2026-07-08",false,"bacteriology","Skin is the body’s largest and thinnest organ which serves as an anatomical barrier between the sterile internal organs and the external environment, which is teemed with microorganisms. Break in the skin surface may result in skin and soft tissue infections. Wound infection can also occur as a complication of surgery, trauma, and bites or diseases that interrupt mucosal or skin surfaces.\n\nWound infections may be caused by one or many organisms depending on the site of the infection. For example, dermatophytes are responsible for infections in the keratinized layer; superficial skin wounds are often caused by aerobes only, while anaerobes are commonly isolated from abscesses of the perineal, inguinal, and buttock area, whereas mixed facultative aerobic organisms cause non-perineal infections. Similarly, postoperative wounds are often infected with a mixture of aerobes and anaerobes. In contrast, deep wound infections, such as internal body or organ infections, can be caused by one or several aerobes and\u002For anaerobes.\n\n> Abscesses are accumulations of pus in tissue and any organism isolated from them may be of significance.\n\nWounds, especially postoperative wounds, may become colonized with potential pathogens. A gram stain is a useful diagnostic tool in determining colonization versus infection. A gram stain showing few or no polymorphonuclear cells with relatively large amounts of normal skin flora are consistent with colonization. However, wound gram stains showing moderate to many polymorphonuclear cells usually indicate infection.\n\n## Possible pathogens in Pus\n\nThis blog post contains information **ONLY** about the isolation and identification of common bacterial isolates (aerobes and facultative anaerobes) from pus aspirate\u002Fswab.\n\n| Gram-positive | Gram-negative |\n| --- | --- |\n| Staphylococcus aureus | Pseudomonas aeruginosa |\n| Streptococcus pyogenes | Escherichia coli |\n| Enterococcus species | P roteus species |\n| Anaerobic streptococci | Klebsiella species |\n| Other streptococci | Bacteriodes species |\n| Clostridium perfringens and other clostridia | Acinetobacter species |\n| Actinomycetes | Other enteric bacilli |\n| Mycobacterium tuberculosis |  |\n| Others |  |\n| Fungi: Histoplsama , Candida, and fungi that cause mycetoma. |  |\n| Parasites: Entamoeba histolytica (in pus aspirated from an amoebic liver abscess) |  |\n| Viruses: Pox viruses and herpes viruses |  |\n\n## Specimen Collection\n\nAs far as possible, collect specimens before antimicrobial therapy and\u002For before applying the antiseptic dressing. The ideal specimen is an aspirate from a previously undrained abscess or a tissue biopsy. Ideally, a minimum volume of 1mL (up to 5 mL) of pus should be collected. Large volumes of purulent material maintain the viability of anaerobes for longer.\n\nThe aspirate should be collected in a sterile syringe; any air bubbles should be expelled. Needle safely and tightly capped (needles should **NOT** be sent).\n\nA tissue specimen should be placed in a sterile universal bottle (or any sterile leakproof container) and sent to the lab for immediate processing if anaerobes are suspected. If there is a delay in transporting, the tissue should be placed in an anaerobic transport system.\n\n![ - Comparison of aspirated pus and swab culture from an infected joint site. Image source: Koneman’s Color Atlas and Textbook of Diagnostic Microbiology](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Fswab-or-Aspirate.png)Figure: Comparison of aspirated pus and swab culture from an infected joint site. Image source: Koneman’s Color Atlas and Textbook of Diagnostic Microbiology\n\nSwabs are less desirable because of the smaller amount of sample specimen and the fact that they are often contaminated with normal skin flora, making interpretation of results difficult. When using swabs, the deepest part of the wound should be sampled, avoiding the superficial microflora. Swabs should be well soaked in pus.\n\n## **Specimen Transport**\n\nLabel the specimen and deliver it to the laboratory as soon as possible with a completed request form. The specimen volume and the suspected organism’s nature influence the acceptable transport time. The recovery of anaerobes is compromised if the transport time exceeds 3hr. Suppose delays in transportation to the laboratory are unavoidable. In that case, samples should be placed in the transport medium ([Amies transport medium](\u002Famies-transport-medium\u002F) or [Cary-Blair transport medium](\u002Fcary-blair-transport-medium-composition-preparation-uses\u002F)) to minimize drying and exposure to oxygen if anaerobes are suspected.\n\n> If processing is delayed, refrigeration is preferable to storage at ambient temperature.\n\n## **Laboratory examination of Pus sample**\n\nHandling clinical specimens, especially pus samples that may contain unknown pathogens, invokes all the foundational microbiology laboratory safety practices. Before collecting, transporting, or processing any specimen, review [microbiology laboratory safety rules](https:\u002F\u002Fmicrobeonline.com\u002Fmicrobiology-laboratory-safety-rules-procedure\u002F) for specimen safety, universal precautions, and exposure protocols\n\n- Describe the appearance of the specimen: Describe the presence or absence of sulfur granules *(needed only for the suspected cases of **mycetoma** or actinomycosis, when requested).*\n- **Preparation of the Smear**\n- If pus swab is sent:\n\nOnly one aerobic pus swab: Inoculate the culture media first before using the swab to make smears for Gram staining If swabs (one anaerobic and two aerobic) are submitted for culture, use the second swab to make gram stain\n\n- If tissue sample is submitted: make a Gram stain from ground tissue.\n- If pus aspirate is sent, place one drop of pus onto a clean microscope slide using a sterile pipette. Spread this using a sterile loop to make a thin smear for Gram staining.\n- **Gram Staining:** Make an evenly spread smear of the specimen on a clean, grease-free slide. Allow the smear to air-dry in a safe place. Heat fix the specimen and stain by [Gram staining technique](\u002Fgram-staining-principle-procedure-results\u002F). Examine the smear for the presence of bacteria and pus cells (PMNs) using 100x objective lens and look especially for:\n\nGram-negative rods (possible pathogens are *E.coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus* or Bacteroides species) [Gram-positive cocci](\u002Fgram-positive-cocci-of-medical-importance\u002F) in pairs, chains or clusters (possible pathogens are Staphylococcus aureus, Streptococcus pyogenes, anaerobic streptococci or enterococci). Gram positive large rods with square ends (possible pathogens are *Clostridium perfringens* or *Bacillus anthracis*).\n\nIn the case of anaerobic infections large number of pleomorphic bacteria (streptococci, Gram positive and Gram negative rods of various sizes and fusiform bacteria) may be seen. Sometimes, Gram-positive yeast cells with pseudohyphae may be seen, which can be *Candida albicans.*\n\n![ - Staphylococcusin Gram Stain](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FGram-stain-of-Staphyloccus.jpg)Figure: Staphylococcus in Gram Stain\n\n## **Pus Culture**\n\nCulture Media: Wound specimens collected on aerobic swabs or pus aspirate should be plated on to the following media:\n\n- **Sheep blood agar** (to isolate *S. aureus* and *Streptococcus* *pyogenes* or other streptococci)\n- **MacConkey agar** (to isolate Gram-negative rods)\n\n**Incubation Condition:**\n\n- **Temperature**: 35ºC -37ºC\n- **Atmosphere**: Blood Agar plate in carbon dioxide enriched atmosphere (e.g. 5% CO2 incubator or in a candle jar) and MacConkey agar plate in ambient air (normal incubator)\n- **Time:** Up to 48 hours (observe the plate after 24 hours of incubation, if growth is seen, do further processing, if not, reincubate for additional 24 hours.)\n\n**Examination and Reporting the Culture results**\n\nIf the growth is seen after 24\u002F48 hours of culture, the colony morphology and identification of the isolates should be examined.\n\nIn the Blood Agar plate, look for hemolysis. *Staphylococcus aureus* and *Streptococcus pyogenes* give beta-hemolysis in Blood Agar (Some *S. aureus* isolates may not show hemolysis).\n\n- *S. aureus* gives yellow to cream or white colonies. Colonies are slightly raised and easily emulsified.\n- *S.pyogenes* produces beta-hemolytic colonies. Colonies are usually small, colorless, dry, shiny, or mucoid.\n- Enterococci give non-hemolytic colonies in blood agar.\n\nWe can differentiate between streptococci and staphylococci by a very simple and rapid test-[Catalase test](\u002Fcatalase-test-principle-uses-procedure-results\u002F) (Staphylococcus-positive, Streptococcus-negative). For identification of suspected *S. aureus* colonies, perform [coagulase test](\u002Fdiagnostic-tests-biochemical-tests-coagulase-test\u002F) (to differentiate coagulase-negative Staphylococci from *S. aureus*) and for suspected Group A Streptococci (*S.pyogenes*) perform [bacitracin sensitivity test](\u002Fbacitracin-test-principle-procedure-expected-results-and-quality-control\u002F) (can be added in the blood agar plate with other antibiotics). If enterococci is suspected perform [bile esculin test.](\u002Fbile-esculin-test-enterococcus-species-principle-procedure-results\u002F)\n\nLook for the growth of lactose fermenter colonies (pink) or non-lactose fermenter colonies (pale) in the MacConkey Agar plate.  Lactose fermenter colonies can be of Escherichia coli, Klebsiella spps, or *Enterobacter* spps and non-lactose fermenter colonies can be of *Psuedomonas aeruginosa,* *Acinetobacter* spp, *Proteus* spps etc.\n\n![ - LF and NLF colonies in MacConkey Agar](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FLactose-fermenting-and-non-lactose-fermenting-colonies.jpg)Figure: LF and NLF colonies in MacConkey Agar\n\nMember of the family **Enterobacteriaceae** can be differentiated from other Gram-negative bacilli by performing two rapid tests (catalase test +ve, and oxidase test –ve). Identifications of the enteric bacteria can be done by using biochemical tests such as **citrate utilization test,** **Triple Sugar Iron (TSI) Agar test**, Sulphite-Indole-Motility (SIM) test, and urease test.\n\n*Pseudomonas aeruginosa* gives large, flat, spreading pale-colored colonies in MacConkey Agar. It is oxidase positive and can be identified by its pigments and\u002For distinctive smell (characteristics of fruity smell).\n\nDepending on the facilities available in the diagnostic laboratories, organisms can be identified using enterotube test or [API-20E test](\u002Fapi-20e-test-system-introduction-procedure-results-interpretations\u002F) or other newer diagnostics tests available for identifying isolates.\n\n## **Antimicrobial Sensitivity Testing**\n\nFor *Streptococcus pyogen*es and Enterococci, antimicrobial sensitivity testing should be done in MHA supplemented with sheep blood. For *S.aureus* and other gram-negative bacilli, [Mueller-Hinton Agar (MHA)](\u002Fmueller-hinton-agar\u002F)is used. The selection of the antibiotics panel depends on the isolated organism. Unless indicated routinely used (or first line), antibiotics should be used. If the patient is in an intensive care unit (SICU, PICU, NICU) or is receiving particular antibiotic, or the isolate is resistant to first-line antibiotics, sensitivity testing should include requested antibiotics and\u002For second-line antibiotics.\n\n**References and further reading**\n\n- [Color Atlas and Textbook of Diagnostic Microbiology](https:\u002F\u002Famzn.to\u002F2vRkUvk), Koneman, 5th edition\n- [Bailey & Scott’s Diagnostic Microbiology](https:\u002F\u002Famzn.to\u002F2WZxPHL), Forbes, 11th edition\n- District Laboratory Practice in Tropical Countries Part-2. Monica Cheesbrough, 2nd edition",[],[46],"specimen-collection-transport",[48,56,63,70,77,100,126,142],{"slug":49,"title":50,"description":50,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":51,"lastUpdatedDate":52,"draft":41,"category":53,"image":37,"faq":54,"tags":55},"blood-collection-tubes","Blood Collection Tubes: Significance of Color Coding","2023-01-26","2026-07-19","lab-equipment",[],[46],{"slug":57,"title":58,"description":58,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":59,"lastUpdatedDate":60,"draft":41,"category":42,"image":37,"faq":61,"tags":62},"rejection-criteria-for-microbiological-specimens","Microbiology Sample Collection Guidelines and Rejection Criteria","2021-05-04","2026-07-05",[],[46],{"slug":64,"title":65,"description":65,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":66,"lastUpdatedDate":60,"draft":41,"category":67,"image":37,"faq":68,"tags":69},"sample-collections-for-laboratory-diagnosis-of-fungal-infections","Sample Collections for Lab Diagnosis of Fungal Infections","2021-04-03","mycology",[],[46],{"slug":71,"title":72,"description":72,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":73,"lastUpdatedDate":60,"draft":41,"category":74,"image":37,"faq":75,"tags":76},"viral-transport-media-vtm","Viral Transport Media (VTM): Preparation, Uses","2020-03-23","culture-media",[],[46],{"slug":78,"title":79,"description":80,"seoTitle":37,"seoDescription":37,"author":81,"createdDate":82,"lastUpdatedDate":60,"draft":41,"category":74,"image":37,"faq":83,"tags":99},"amies-transport-medium","Amies Transport Medium: Composition, Uses, and Why It Replaced Stuart's Medium","Why a fragile gonococcus swab can die before it ever reaches the lab, the design fix that made Amies better than Stuart's medium, and when to choose the charcoal-free version instead.","Nisha Rijal","2019-12-03",[84,87,90,93,96],{"question":85,"answer":86},"What is Amies transport medium used for?","Preserving swab specimens, such as throat, wound, vaginal, and genital swabs, in a stable, non-multiplying state during transport to the microbiology laboratory.",{"question":88,"answer":89},"Why did Amies medium replace Stuart's medium?","Stuart's medium used glycerophosphate as a buffer, but some organisms could use it as a carbon source and keep multiplying during transport. Amies replaced it with an inorganic phosphate buffer to remove that problem.",{"question":91,"answer":92},"When should Amies without charcoal be used instead of the charcoal version?","Specifically for Mycoplasma and Ureaplasma recovery, since charcoal, helpful for most other fastidious organisms, actually inhibits recovery of these two.",{"question":94,"answer":95},"Can Amies transport medium be frozen for longer storage?","No. Freezing causes ice crystals to rupture bacterial cells, killing the organism. Refrigeration, not freezing, is the correct way to slow deterioration during transport.",{"question":97,"answer":98},"How long can a specimen sit in Amies medium before processing?","Ideally within 6 hours, and no later than 24 hours, maintaining a cold chain throughout.",[46],{"slug":101,"title":102,"description":103,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":104,"lastUpdatedDate":60,"draft":41,"category":105,"image":37,"faq":106,"tags":125},"lab-diagnosis-intestinal-parasitic-infections","Laboratory Diagnosis of Intestinal Parasitic Infections: Methods, Specimen Handling, and When to Use Each Test","Complete guide to laboratory diagnosis of intestinal parasites — stool collection, O&P examination, concentration techniques, permanent stains, culture, serology, and PCR with a decision table and specimen exceptions for pinworm and Schistosoma.","2018-11-13","parasitology",[107,110,113,116,119,122],{"question":108,"answer":109},"What is the O&P examination for intestinal parasites?","The Ova and Parasite (O&P) examination is the standard laboratory protocol for diagnosing intestinal parasitic infections. It consists of four sequential steps: macroscopic examination of the stool, direct saline and iodine wet mount (for motile trophozoites and helminth eggs), a concentration technique (formal-ether sedimentation or Kato-Katz), and a permanent stained smear (trichrome or iron-haematoxylin) when protozoan identification is required. Each step detects organisms that the others may miss.",{"question":111,"answer":112},"Why must liquid stool be examined within 30 minutes?","Liquid stool from patients with acute diarrhoea may contain trophozoites of Entamoeba histolytica or Giardia lamblia. Trophozoites are motile and identifiable by their characteristic movement, but they disintegrate rapidly after passage. After 30 minutes, motility is lost and trophozoites degenerate, making identification unreliable. Formed stool (containing cysts and eggs, which are more stable) can be examined within 24 hours.",{"question":114,"answer":115},"Why is pinworm not diagnosed from a routine stool O&P examination?","Enterobius vermicularis (pinworm) females migrate from the rectum to the perianal skin at night to deposit eggs. These eggs are rarely shed into the stool in detectable numbers. The correct diagnostic method is the cellophane (Scotch) tape test: transparent adhesive tape is pressed against the perianal skin early in the morning before bathing and applied to a glass slide for microscopic examination. This has far higher sensitivity than stool O&P for pinworm diagnosis.",{"question":117,"answer":118},"What stain is used to diagnose Cryptosporidium in stool?","Cryptosporidium parvum oocysts are acid-fast and are not detected by routine direct wet mount or trichrome staining. A modified acid-fast stain (modified Ziehl-Neelsen or Kinyoun) is required — oocysts appear as pink-red spheres against a blue background. The same stain detects Cyclospora cayetanensis and Cystoisospora belli. This stain must be specifically requested and is especially important in HIV\u002FAIDS patients with unexplained chronic diarrhoea.",{"question":120,"answer":121},"What is the difference between formal-ether sedimentation and Kato-Katz technique?","Formal-ether sedimentation concentrates cysts, eggs, and larvae from a stool sample using formalin fixation and ethyl acetate, suitable for detecting all intestinal parasites including protozoa (but not trophozoites). Kato-Katz uses a large, standardised stool volume pressed through a mesh screen onto a slide for quantitative helminth egg detection — it gives eggs per gram (EPG) of stool, useful for measuring infection intensity and treatment response. Kato-Katz detects helminth eggs only and cannot identify protozoa.",{"question":123,"answer":124},"How many stool specimens are needed to diagnose giardiasis?","A minimum of three stool specimens collected on separate days is recommended for most intestinal parasites. For Giardia lamblia and Entamoeba histolytica, six specimens are preferred because cyst shedding is intermittent — a single specimen misses up to 30% of infections. If clinical suspicion remains high after negative results, stool antigen EIA for Giardia offers higher sensitivity than repeated microscopy.",[46],{"slug":127,"title":128,"description":129,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":130,"lastUpdatedDate":60,"draft":41,"category":74,"image":37,"faq":131,"tags":141},"alkaline-peptone-water-apw-principle-preparation-uses","Alkaline Peptone Water (APW): Composition, Principle, Preparation, and Uses in Vibrio Enrichment","Alkaline Peptone Water (APW) is the standard enrichment broth for Vibrio cholerae isolation. Learn its pH selectivity principle, why vibrios form a pellicle at the surface, how to subculture onto TCBS agar, and when APW is used versus Cary-Blair transport medium.","2016-09-10",[132,135,138],{"question":133,"answer":134},"Why does Vibrio cholerae form a pellicle at the surface of APW, and why is only the surface subcultured onto TCBS?","V. cholerae is both motile (single polar flagellum) and aerophilic — it preferentially grows in oxygenated environments. When inoculated into APW and incubated at 37°C, V. cholerae actively swims toward the air-liquid interface where oxygen concentration is highest, accumulating there and forming a thin film called a pellicle after 4–6 hours. Competing organisms that survive the alkaline pH but lack directed motility toward the surface tend to remain distributed throughout the broth or settle to the bottom. Inoculating TCBS agar from the surface pellicle only — by touching the inoculating loop to the surface without mixing or shaking the broth — transfers V. cholerae-enriched material while leaving the sediment of competing organisms behind. Mixing the broth before subculture defeats the purpose of this spatial separation and reduces the sensitivity of the enrichment step.",{"question":136,"answer":137},"Why is APW suitable for Vibrio enrichment but unsuitable for Salmonella, Shigella, or Campylobacter?","APW's selectivity is based entirely on its alkaline pH (8.6–9.0). This pH range is optimal for V. cholerae and selectively suppresses most intestinal commensals. However, it also inhibits the growth of other clinically important enteric pathogens: Salmonella and Shigella grow optimally at pH 7.0–7.4 and are significantly inhibited at pH 8.6–9.0; Campylobacter is microaerophilic and also pH-sensitive, with optimal growth at pH 6.5–7.5. If a specimen for broad enteric workup (including Salmonella, Shigella, or Campylobacter) is placed into APW for transport, these organisms will be progressively killed by the alkaline pH while V. cholerae multiplies. The specimen will arrive at the laboratory as effectively Vibrio-only material, making it impossible to detect co-infecting pathogens or to perform a comprehensive enteric culture. Cary-Blair transport medium, which is pH-neutral to mildly alkaline and contains no selective enrichment mechanism, preserves all enteric pathogens simultaneously.",{"question":139,"answer":140},"When is APW enrichment unnecessary, and why?","APW enrichment is unnecessary when the specimen contains very high numbers of V. cholerae — specifically in acute cholera during the first few days of illness. A patient with acute cholera is passing liquid 'rice-water' stool containing 10⁷ to 10⁹ V. cholerae per milliliter. At these concentrations, V. cholerae vastly outnumbers competing flora even before enrichment, and direct plating onto TCBS agar will produce abundant yellow colonies without any pre-enrichment step. Proceeding with APW enrichment in this situation delays the result by 6–8 hours unnecessarily. APW enrichment is specifically valuable for the four situations where organism counts are low: convalescent patients (illness >5 days, declining shedding), asymptomatic carriers, environmental water and food samples, and rectal swab specimens (which transfer fewer organisms than fresh liquid stool).",[46],{"slug":143,"title":144,"description":145,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":130,"lastUpdatedDate":60,"draft":41,"category":74,"image":37,"faq":146,"tags":156},"cary-blair-transport-medium-composition-preparation-uses"," Cary-Blair Transport Medium: Composition, Principle, Preparation, and Uses","Cary-Blair is the medium of choice for transporting enteric pathogens including Vibrio cholerae, Salmonella, Shigella, and Campylobacter. Learn its principle, semisolid composition, survival times for key organisms, and how it compares to Stuart's, Amies, and APW.",[147,150,153],{"question":148,"answer":149},"Why does Cary-Blair medium use sodium thioglycollate when other transport media do not?","Sodium thioglycollate is a reducing agent that lowers the oxidation-reduction (redox) potential of Cary-Blair medium, creating a microaerobic to anaerobic microenvironment within the semisolid matrix. This is specifically important for two groups of pathogens: (1) Campylobacter species, which are microaerophilic and are killed by prolonged exposure to atmospheric oxygen concentrations — the reduced environment extends their viability during transport; and (2) any facultative anaerobes present in the specimen whose viability is compromised by reactive oxygen species accumulation at room temperature. Stuart's and Amies media do not contain thioglycollate, which is why they show inferior Campylobacter recovery compared to Cary-Blair for specimens with anticipated transport delays beyond 2 hours.",{"question":151,"answer":152},"Why is Cary-Blair medium alkaline (pH 8.4), and how does this protect the specimen?","The alkaline pH of 8.4 in Cary-Blair medium serves two protective functions. First, it creates conditions that specifically favour Vibrio cholerae survival — V. cholerae grows optimally at pH 8.0–9.6 and survives transport far better in alkaline than neutral conditions. This is why Cary-Blair is the medium of choice for cholera specimen transport and is superior to Stuart's and Amies media (both pH 7.3) for this specific organism. Second, the alkaline pH acts as a buffer against the metabolic acid production that would otherwise occur as organisms undergo limited metabolic activity during transport. Even minimal metabolism of substrates in the specimen produces organic acids; at pH 7.3, these acids accumulate and can drop the local pH to levels lethal to acid-sensitive organisms such as Shigella. The alkaline starting pH provides a substantial buffer capacity that maintains a safe pH range throughout the transport period.",{"question":154,"answer":155},"How long do different enteric pathogens survive in Cary-Blair medium, and what are the practical implications?","Survival times in Cary-Blair medium vary significantly by organism, which has direct implications for transport planning: Salmonella and Shigella survive for at least 48 hours and typically several days; Vibrio cholerae survives for at least 48 hours, with Cary-Blair's alkaline pH providing superior conditions compared to other transport media; Yersinia enterocolitica and Y. pestis survive for 48+ hours; Campylobacter species survive for only up to 6 hours, making same-day transport essential — specimens for Campylobacter culture collected in Cary-Blair must reach the laboratory within 6 hours, or be refrigerated to slow all bacterial activity. The practical implication for field collection: Cary-Blair is suitable for overnight transport for Salmonella and Shigella, but not for Campylobacter. If Campylobacter is specifically suspected and same-day transport is not possible, campy thioglycollate medium is the alternative.",[46],[158,164,171,176,180,184,189,194,198,202],{"slug":159,"name":38,"description":160,"image":161,"body":162,"postCount":163},"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.*",433,{"slug":165,"name":166,"description":167,"image":168,"body":169,"postCount":170},"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.",81,{"slug":172,"name":173,"description":174,"image":37,"body":37,"postCount":175},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":177,"name":178,"description":174,"image":37,"body":37,"postCount":179},"samikshya-acharya","Samikshya Acharya",20,{"slug":181,"name":182,"description":174,"image":37,"body":37,"postCount":183},"alisha-tripathi","Alisha Tripathi",6,{"slug":185,"name":186,"description":187,"image":37,"body":37,"postCount":188},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":190,"name":191,"description":192,"image":37,"body":37,"postCount":193},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":195,"name":196,"description":174,"image":37,"body":37,"postCount":197},"srijana-khanal","Srijana Khanal",18,{"slug":199,"name":200,"description":192,"image":37,"body":37,"postCount":201},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":203,"name":81,"description":174,"image":37,"body":204,"postCount":205},"nisha-rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]