Finding the right tests…
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Finding the right tests…
Microbiology
A stool culture grows a sample of your stool in the lab to look for specific bacteria that cause gastroenteritis, such as Salmonella, Shigella, or Campylobacter. It's different from a routine stool exam, which looks at the sample under a microscope for things like blood cells or parasites without growing anything. Your doctor typically orders a culture when diarrhea comes with fever, blood or mucus in the stool, severe cramping, or lasts long enough to rule out a simple viral stomach bug, since bacterial gastroenteritis is treated differently and sometimes needs antibiotics that a virus would not.
This test identifies which, if any, disease-causing bacteria are present in your stool, distinguishing them from the normal bacteria that live in every healthy gut. Campylobacter is the most frequently identified bacterial cause of diarrheal illness, alongside Salmonella and Shigella, and the specific organism found changes whether antibiotics help at all, since some bacterial diarrheas resolve on their own while others need targeted treatment. A separate test looks for E. coli strains that produce toxins, since these need different handling in the lab than the bacteria a standard culture targets.
A routine stool exam looks at your sample under a microscope for blood, white cells, or parasites, but it doesn't grow bacteria or identify a specific species. A culture is the step that actually names which bacteria, if any, are causing the illness, which matters because treatment differs by organism.
Most viral stomach bugs pass within a few days without needing this test. A culture becomes useful when diarrhea comes with fever, visible blood or mucus, severe abdominal pain, or lasts unusually long, since these features raise the chance a specific bacteria is responsible rather than a self-limited virus.
A portion of stool is placed on growth media that favors disease-causing bacteria over the normal flora already present in the gut. Any colonies that grow are identified by species, and disease-causing organisms are then tested against antibiotics to see which would work, since not every bacterial cause needs or benefits from antibiotic treatment.
A negative culture means none of the bacteria tested for were found, which points toward a viral cause or a bacteria not covered by the standard panel, such as toxin-producing E. coli, which needs a separate test. Your doctor decides whether further testing is worth pursuing based on how you're doing.
A routine stool test looks at the sample under a microscope for things like blood cells or parasites but doesn't grow bacteria. A stool culture grows the sample specifically to identify disease-causing bacteria by species.
Not usually. Most short, mild diarrhea is viral and clears on its own without needing a culture. Your doctor is more likely to order one if there's fever, blood in the stool, severe pain, or symptoms that won't let up.
You'll be given a clean container or kit to collect a stool sample without mixing in urine or toilet water. Ask your doctor or the centre for specific instructions and how quickly to bring it in.
No. Some bacterial causes of diarrhea, once identified, are still best managed with fluids and rest rather than antibiotics, since treatment can depend on the specific organism and your overall condition. Your doctor decides based on the result and how you're doing.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
A standard bacterial culture targets bacteria specifically. If a parasite is suspected, your doctor typically requests a separate stool exam for ova and parasites alongside or instead of a culture.
It means the bacteria tested for weren't found, which can point to a virus, a bacteria outside the standard panel, or a non-infectious cause. Your doctor may consider further testing depending on how your symptoms progress.