What Are Stool Cultures?

Stool cultures are an effective way to identify diseases of the digestive system associated with infections. In fact, they are a common way of conducting various scientific studies that conclude the presence of bacteria and parasites in the gut.

We often become infected with parasites, viruses and bacteria that cause various symptoms of intestinal malaise. A number of conditions are also manifested by bleeding in the stool, such as colitis, stomach cancer and stomach ulcers. A stool culture is therefore the mandatory screening test.

Microbiological cultures

Microbiological culture is a method based on the multiplication of microorganisms in a sterile medium, usually bacteria, to facilitate the detection of a disease causing disease. In short, it is to give microorganisms the ideal environment for their development.

The planting of biological samples from the patient comes from sputum, saliva rub, skin parts and also feces. Scientists place them in small containers called petri dishes, with a solid in them containing agar.

Many pathogens have specific growth requirements, so each culture medium is specialized based on the microorganism sought, as reported by this portal specialized in immunology. Some of these parameters are as follows:

• Availability of nutrients suitable for bacterial growth.
• Presence or absence of oxygen and other gases.
• Sufficient humidity conditions.
• Ambient light.
• Acidity or alkalinity.

• Temperature.
• Sterility of the environment.

Depending on the types of microorganisms you want to find, the conditions in the culture media should be different. Once there is growth on the plate, experts isolate samples under a microscope to identify the specific species causing the disease.

As various scientific sources indicate, there are many different types of stains for the identification of bacteria. Experts place a dye in the stain that the microorganisms absorb, giving them that color. The most common medical use is Gram-type staining.

What are stool cultures?

A stool culture is nothing more than a microbiological culture based on collecting stool as a sample from a sick patient. It is mainly used to study cases of persistent or recurrent diarrhea for no known reason.

As this medical review article states (Spanish link), the collection of fecal samples in infectious bowel disease that does not resolve within two or three days is necessary. Some of the pathogenic microorganisms that can be identified by stool cultures are:

• Salmonella
• Campylobacter
• Helicobacter
• Shigella, Yersinia
• Clostridium difficile
• Staphylococcus aureus

Collection of samples

The review article we cite illustrates the steps to be taken to collect the sample from the stool culture. We describe it below:

• The patient provides a sample in a wide container with an airtight seal, with a minimum sample volume of two to four grams in pasty stool and five to ten milliliters in liquid stool.
• Fecal samples that have been exposed to the environment for two hours or more, or that are contaminated with urine or toilet paper residue, are not usable.
• Scientists take a very small sample from the patient’s stool and plant it in a culture medium suitable for the growth of pathogenic microorganisms.

• If the first sample does not detect the presence of enteropathogens, it is necessary to collect two more samples on different days.
• Once the pathogenic bacteria are identified, the appropriate antibiotic is prescribed.

What is needed to observe stool cultures?

Scientists use these microbiological cultures to identify various diseases by identifying bacteria, planting and staining the fecal sample. They also investigate possible eggs or parasite residues.

According to the Center for Disease Control and Prevention , parasites such as tapeworms are identified with stool cultures because their eggs are seen in the patient’s stool. Likewise, if they don’t immediately detect hidden blood in the stool, a biochemist can detect it.

Restrictions of stool cultures

Not everything is ideal in the world of microbiological cultivation. Results are not always possible and are largely dependent on the quality of the sample. As this scientific article states, there are certain risks in identifying diseases through stool cultures.

First , scientists cannot routinely search for all enteropathogens. Since the culture medium is specific to the microorganisms you want to find, some grow less frequently, such as Bacteroides fragilis, Edwarsiella tarda or Escherichia alberti.

There are also unknown pathogens whose biological requirements are unknown. They may therefore not multiply, because they do not have the right conditions for it. This goes beyond the clinical situation in time, in which the aim is to detect the most common diseases.

Other studies state that stool cultures are not suitable for people who have been hospitalized for more than three days.

This is because the cause of diarrhea is not due to pathogens in the gut. In these cases, the most suitable method is the PCR detection technique. This identifies specific genes of a microorganism in the fecal sample.

Stool cultures: what to remember?

These microbiological cultures are useful in identifying pathogenic gut bacteria, parasites and also blood in the stool. However, due to the high cost and delay of the procedure, only patients with specific epidemiological problems can receive it.

However, if you need to give a stool sample at the hospital, don’t worry. Doctors will try to pinpoint the cause of gastrointestinal illness so that they can administer the right medicine.