Stool Culture: Understanding Your Report

Section Editor: Rodney E. Rohde PhD
June 3, 2026

A stool culture is a laboratory test that looks for disease-causing bacteria in a stool sample (also called feces or a bowel movement). It is most often used to find the cause of severe, long-lasting diarrhea that contains blood. The gut normally contains enormous numbers of harmless bacteria, so a stool culture is designed to search specifically for the few types of bacteria known to cause illness. A bacterium is a microorganism, a living thing too small to see without a microscope.

This article explains what a stool culture looks for, what the wording on your report means, and how it differs from other stool tests, so you can better understand a report you have received.

What is a stool culture, and why is it done?

An infection of the digestive tract, also called a gastrointestinal infection or gastroenteritis, is a common cause of diarrhea, cramping, and sometimes fever. Many of these infections are caused by viruses and resolve on their own, so a stool culture is not needed in most cases of diarrhea.

A stool culture is usually ordered only in specific situations, such as severe, bloody diarrhea that lasts more than a few days; diarrhea with a high fever; recent travel; a weakened immune system; or when an outbreak is suspected. In these situations, identifying the bacterium responsible helps guide both treatment and any public health steps that may be needed.

What a stool culture looks for

Because the gut is full of normal, harmless bacteria (called normal flora), the laboratory does not report every bacterium it finds. Instead, it searches for a standard group of disease-causing bacteria, most commonly:

Salmonella — A common cause of diarrhea, often linked to contaminated food.
Shigella — A cause of diarrhea that may contain blood.
Campylobacter — One of the most common bacterial causes of diarrhea.
Certain types of E. coli — Especially a group that produces a toxin and can cause bloody diarrhea, sometimes written on reports as STEC or E. coli O157.

Some other bacteria are not part of this standard search and are tested for only when specifically requested or suspected, for example, after travel to certain regions.

Molecular stool tests (PCR panels)

Many laboratories now use molecular tests, which look for the genetic material of many germs at once, including bacteria, viruses, and parasites, from a single sample. These tests are explained in the article on PCR, antigen, and antibody tests. They are fast and highly sensitive, and they can identify causes that a culture might miss. A traditional culture is still useful, however, because it grows the actual bacteria, which can then be tested against antibiotics if treatment is needed.

Other stool tests that are not a culture

It is easy to assume that a stool culture checks for everything, but two common stool tests are usually done separately:

Clostridioides difficile (C. diff) testing — A separate test that looks for a specific bacterium and the toxin it produces, usually considered after recent antibiotic use. It is explained in the article on C. difficile testing.
Ova and parasites (O&P) — A separate test in which the stool is examined under a microscope for parasites and their eggs. It is explained in the article on OVA and parasite testing.

If your symptoms suggest one of these, your doctor may order the corresponding test in addition to or instead of a stool culture.

How to read your result

The wording on your report depends on what was found and which test was used.

No pathogen isolated, or normal flora — No disease-causing bacteria from the standard group were found, and only normal gut bacteria grew. This is a common and reassuring result.
A named bacterium isolated — A specific disease-causing bacterium grew, such as Salmonella, Shigella, or Campylobacter, identifying the cause of the infection.
Molecular test: detected or not detected — The genetic material of one or more specific germs was, or was not, found.

A result of no growth does not completely rule out an infection. Many cases of diarrhea are caused by viruses, which a stool culture does not detect, and some infections clear before the sample is tested.

Antibiotics and what happens after

A stool culture describes what was found and informs the decisions you and your healthcare team make together, rather than dictating them on its own.

Most cases of infectious diarrhea resolve on their own, and the most important treatment is staying hydrated; antibiotics are not needed for many of these infections. When a specific bacterium is identified, your doctor decides whether antibiotics are appropriate, sometimes using susceptibility testing to determine which antibiotics will work, as explained in the article on culture and sensitivity testing. For some infections, especially toxin-producing E. coli, antibiotics are usually avoided because they can increase the risk of serious complications. Several of these infections are also reportable to public health authorities, who track them to find and stop outbreaks, so you may be contacted as part of that process.

Questions to ask your doctor

Did my stool culture find a specific bacterium, and which one?
Does a result of “normal flora” or “no pathogen” mean I do not have an infection?
Could my diarrhea be caused by a virus or by something a stool culture does not detect?
Should I also be tested for C. difficile or for parasites?
Do I need antibiotics, or will this get better on its own?
Are there any infections where antibiotics should be avoided?
How can I avoid spreading this to others at home?
Will my infection be reported to public health, and what does that mean for me?
What symptoms, such as signs of dehydration or blood in the stool, should prompt me to seek care urgently?
Who should I contact if I am not improving?