Test : Stool Culture, Diarrheagenic E.coli
Indications : Ideally the stool culture test for E.coli must be ordered for all patients with bloody
diarrhea. In case of outbreak, the test can even be done with watery stools which are not bloody. If EHEC is suspected, then the stool sample must be obtained as early as possible as it may be impossible to isolate enterohemorrhagic E.coli at a later stage.
E.coli is a part of the normal fecal flora and hence laboratories must be specifically instructed to detect pathogenic E.coli. Stool culture using sorbitol MacConkey medium is the standard diagnostic method.
Stool samples can be obtained by inserting a preservative-dipped cotton swab into the rectal region and by rotating it gently. It is then placed in a sterile container and transported to the laboratory as quickly as possible. The sample is streaked on to culture plates containing specific media that facilitates the growth of E.coli such as sorbitol MacConkey medium.
Physiology : This stool culture test is carried out to detect the presence of Diarrheagenic E.coli.
Most of the time
E.coli exists as normal parasites in human intestines. Some strains, however, are pathogenic and cause severe illnesses. It is a common cause of
food poisoning and
travelers’ diarrhea.
The following are the four major categories of Diarrheagenic E.coli -
• Enterotoxigenic (ETEC) - Travelers’ diarrhea and infant diarrhea in less developed countries
• Enteropathogenic (EPEC) - Infant diarrhea
• Enterohemorrhagic (EHEC) - Hemorrhagic colitis, Hemolytic uremic syndrome, Thrombotic thrombocytopenia purpura.
• Enteroinvasive (EIEC) - Dysentery
Normal Range : Normal colinc flora
Interpretation : Normal
Negative - Only normal flora present
Abnormal
Positive - Pathogenic E.coli are seen in the culture indicating enteritis due to these pathogens.
Sample : Rectal swab, fresh stool
Test Method : culture in macconkey agar.
Related Tests : Methylene blue stain, Stool culture
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