Which pathogen displays attaching and effacing lesions via a Type III secretion system and is common in infants in developing countries causing watery diarrhea?

• A. Shigella dysenteriae
• B. Enteroaggregative E. coli (EAEC)
• C. Enteropathogenic E. coli (EPEC) displays attaching and effacing lesions via a Type III secretion system; common in infants in developing countries causing watery diarrhea.
• D. Enterotoxigenic E. coli (ETEC)

Answer: (C)

Attachment and effacing lesions produced through a Type III secretion system are a defining feature of Enteropathogenic E. coli. In this pathogen, the Type III secretion system injects proteins into intestinal epithelial cells, causing the actin cytoskeleton to rearrange and microvilli to be effaced, while the bacteria pedestal-attach to the cell surface. This disruption of the absorptive surface leads to watery diarrhea, a common presentation in infants in developing countries. Other pathogens differ in their mechanism: Shigella invades and damages the mucosa causing dysentery with blood; enteroaggregative E. coli adheres in a stacked-brick pattern and forms biofilms; enterotoxigenic E. coli causes secretory watery diarrhea via toxins but does not create attaching/effacing lesions.