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For the most part, laboratories use microbiology tests -- similar to microbiological blood tests -- to determine if disease-causing microorganisms are present. Three main types of microbiological tests are commonly performed on feces:- Antibody-antigen type tests, that look for a specific virus
- Microscopic examination for intestinal parasites and their eggs (ova)
- Routine culture.
Routine culture involves streaking the sample onto agar plates containing special additives, such as MacConkey's Agar, which will inhibit the growth of Gram-positive organisms and will selectively allow enteric pathogens to grow. These pathogens are incubated for a period, and the bacterial colonies observed.
The main pathogens that are commonly looked for in feces include:- Salmonella and Shigella
- Yersinia
- Campylobacter
- Aeromonas
- Candida (if the patient is immunosuppressed e.g. AIDS or cancer treatment)
- E. coli O157 (if blood is visible in the stool sample.)
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