USMLE Answer 58

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58. The correct answer is E. Urinary tract infections are the most common bacterial infections encountered during pregnancy, and Escherichia coli is the most commonly isolated organism. In the U.S., 70% of cases are caused by P pili-positive strains.

Bundle-forming pili (choice A) are found in enteroaggregative E. coli (EAEC).

GVVPQ fimbriae (choice B) are found in EAEC.

Heat labile toxins (choice C) are pathogenic factors in enterotoxic strains (ETEC).

Heat stable toxins (choice D) are pathogenic factors in ETEC or EAEC.

Type 1 pili (choice F) are a major pathogenic factor in ETEC.