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Clinical microbiology review: Gastrointestinal infections

Stephen B Calderwood, MD
Section Editor
Daniel J Sexton, MD
Deputy Editor
Allyson Bloom, MD


Although the Gram's stain is a first step in the examination of most specimens, only rarely can it be used to distinguish enteric pathogens from normal stool flora. Thus a variety of culture media, biochemical reactions, serological grouping, polymerase chain reaction (PCR) amplification, and other tests must be used to identify the bacteria that cause gastrointestinal infection (picture 1A-C).

Microscopic examination, on the other hand, is the principal method for diagnosing intestinal protozoal and helminthic infection (picture 2).


A 4 year-old girl has fever and dysentery. What does the methylene blue stain of stool show? Question: (picture 3). Answer: (picture 4).


A 24 year-old man develops fever and diarrhea. What does the Gram's stain of stool show? Question: (picture 5). Answer: (picture 6A-B).


A 72 year-old woman from a nursing home presents with abdominal pain and bloody diarrhea. What does the stool culture on sorbitol-MacConkey agar show? Question: (picture 7). Answer: (picture 8).

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Literature review current through: Sep 2017. | This topic last updated: Aug 03, 2017.
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