Enteropathogenic E. coli (EPEC) produces characteristic attaching and effacing lesions on small intestinal epithelium. Which statement correctly describes the molecular interaction central to this lesion?

• A Ipa proteins trigger actin polymerization at one pole of the bacterium
• B Bundle-forming pili bind ganglioside GM1 receptors on the brush border
• C Type IV pili mediate twitching motility along the epithelial surface
• D Intimin on the bacterial surface binds Tir, a bacterial protein translocated into the host cell membrane ✓

Explanation

EPEC uses a type III secretion system encoded on the LEE pathogenicity island to inject its own receptor, Tir (translocated intimin receptor), into the host cell membrane. Intimin, an outer membrane adhesin on the bacterium, then binds Tir, triggering actin accumulation, pedestal formation, and effacement of microvilli. Bundle-forming pili mediate initial loose aggregation but not the defining lesion. Ipa proteins belong to Shigella invasion machinery, and actin tail motility is a feature of Listeria and Shigella, not EPEC.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.