What this test measures
A stool culture and sensitivity test inoculates a fresh stool sample onto selective and differential agar media designed to grow common enteric pathogens — Salmonella (including typhi), Shigella, Vibrio, Campylobacter, enteropathogenic E. coli, Aeromonas, Plesiomonas, Yersinia. Normal gut flora is overwhelmingly present in stool, so the lab relies on selective media to suppress these and let the pathogen grow.
After 24–72 hours, suspicious colonies are identified by biochemistry, MALDI-TOF or serotyping (Salmonella, Shigella). Antibiotic susceptibility is reported on confirmed pathogens.
Why it matters
In India, bacterial diarrhoea remains common — particularly enteric fever (Salmonella Typhi / Paratyphi), shigellosis, and travellers / monsoon-season outbreaks. Most acute watery diarrhoea is self-limited and does not need a culture. A stool culture is indicated when:
• Diarrhoea is bloody, mucus-rich, or febrile (dysentery) • Symptoms last > 7 days • Outbreak settings or food-poisoning investigation • Immunocompromised host • Recent travel or hospitalisation • Suspected enteric fever in a febrile patient
Increasing fluoroquinolone resistance in Salmonella Typhi makes susceptibility testing critical for guiding treatment.
How to prepare
Collect a fresh stool sample in the clean, dry, leak-proof container from the lab. Sample the most abnormal portion (mucus, blood, watery). Avoid contamination with urine or toilet water. Send within 1–2 hours; if delayed, refrigerate (do not freeze). For rectal swab samples (in very young children or non-cooperative patients), use a sterile swab inserted into the anal canal and rotated. Avoid antibiotics for 7 days before if possible. Mention recent travel, food history, and antibiotic use.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Stool Culture (—)[1][2] | Normal gut flora only — no pathogen | No pathogen — bacterial cause unlikely. Viral, parasitic, or non-infectious causes possible. Consider stool R/M + ova-and-parasite, viral antigens, C. difficile testing. | Pathogen identified. Common Indian isolates: Salmonella Typhi / Paratyphi (enteric fever), non-typhoidal Salmonella, Shigella species (dysentery), Vibrio cholerae (outbreak), Campylobacter, Aeromonas, EPEC / EAEC / EIEC in children. |
| Antibiotic Susceptibility (—) | N/A | Susceptible — drug will work. | Resistant — switch to a tested alternative. Indian Salmonella Typhi is increasingly fluoroquinolone-resistant; azithromycin, ceftriaxone, or carbapenems are now first-line in many areas. |
Common stool culture pathogens and treatment
| Organism | Clinical syndrome | Typical first-line therapy |
|---|---|---|
| Salmonella Typhi | Enteric fever | Ceftriaxone, azithromycin (resistance-led) |
| Non-typhoidal Salmonella | Gastroenteritis | Usually supportive; antibiotics if severe |
| Shigella species | Bacillary dysentery | Ciprofloxacin or azithromycin (sens-led) |
| Vibrio cholerae | Cholera (rice-water diarrhoea) | Rehydration + doxycycline / azithromycin |
| Campylobacter jejuni | Bloody diarrhoea | Azithromycin if antibiotics needed |
| Aeromonas / Plesiomonas | Diarrhoea after water exposure | Fluoroquinolone (sens-led) |
Frequently asked questions
When should I do a stool culture?
Indicated when diarrhoea is bloody / mucus-rich / febrile (dysentery), lasts more than 7 days, occurs in outbreaks or immunocompromised hosts, or when enteric fever is suspected.
How do I collect a stool sample?
Pass stool onto a clean dry surface (cling film over the toilet works), use the scoop in the lab kit to transfer a thumb-sized portion into the container. Include mucus or blood if present.
How long does the report take?
48–72 hours for routine bacterial culture and sensitivity. Enteric fever may be confirmed faster on blood culture (often positive in week 1) than stool culture (positive in week 2–3 of illness).
Is stool culture useful for enteric fever (typhoid)?
Yes, but it is most sensitive in the second and third weeks of illness. Blood culture is more sensitive in the first week; bone marrow culture is most sensitive overall but rarely done.
My stool culture is negative but I still have diarrhoea — what next?
Consider parasitic causes (stool ova-and-parasite, Giardia / amoeba antigen tests), viral causes (rotavirus, norovirus PCR), C. difficile (in antibiotic-exposed patients), and non-infectious causes (IBD, IBS, malabsorption).
Will I need antibiotics for most diarrhoea?
No. Most acute watery diarrhoea is self-limited and managed with rehydration alone. Antibiotics are reserved for dysentery, enteric fever, cholera in outbreak settings, severe cases, and immunocompromised hosts.
How fresh does the sample need to be?
Within 1–2 hours of passing is ideal. If transport is delayed, refrigerate (4°C) — do not freeze. Some labs use specific transport media (Cary-Blair) for longer transport.
Related Microbiology / Urine / Stool tests
Tests commonly ordered alongside STOOL C/S, or that help interpret an unexpected result.
Sources & references
- IDSA — Infectious Diarrhea Clinical Practice Guidelines · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Stool Culture · accessed 2026-05-30T00:00:00.000Z
- CDC — Foodborne Illness Surveillance · accessed 2026-05-30T00:00:00.000Z
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