The Longus type IV pilus of enterotoxigenic Escherichia coli (ETEC) mediates bacterial self-aggregation and protection from antimicrobial agents

Enterotoxigenic Escherichia coli (ETEC) strains are leading causes of childhood diarrhea in developing countries. ETEC pili and non-pili adherence factors designated colonization surface antigens (CSA) are believed to be important in the pathogenesis of diarrhea. Longus, a type IV pilus identified as the CSA₂₁, is expressed in up to one-third of ETEC strains, and share similarities to the toxin-coregulated pilus of Vibrio cholerae, and the bundle-forming pilus of enteropathogenic E. coli. To identify longus phenotype and possible function, a site-directed mutation of the lngA major subunit gene in the E9034A wild type ETEC strain was constructed. Lack of longus expression from the lngA mutant was demonstrated by immunoblot analysis and electron microscopy using specific anti-LngA antibody. Formation of self-aggregates by ETEC was shown to be dependent on longus expression as the lngA mutant or wild type grown under poor longus expression conditions was unable to express this phenotype. Longus-expressing ETEC were also associated with improved survival when exposed to antibacterial factors including lysozyme and antibiotics. This suggests that longus-mediated bacterial self-aggregates protect bacteria against antimicrobial environmental agents and may promote gut colonization.