Abstract
ABSTRACTEnteropathogenic Escherichia coli (EPEC) remains a significant cause of infant diarrheal illness and associated morbidity and mortality in developing countries. EPEC strains are characterized by their ability to colonize the small intestines of their hosts by a multistep program involving initial loose attachment to intestinal epithelial cells followed by an intimate adhesion phase. The initial loose interaction of typical EPEC with host intestinal cells is mediated by bundle-forming pili (BFP). BFP are type 4b pili (T4bP) based on structural and functional properties shared with T4bP expressed by other bacteria. The major structural subunit of BFP is called bundlin, a T4b pilin expressed from the bfpA gene in the BFP operon, which contains three additional genes that encode the pilin-like proteins BfpI, BfpJ, and BfpK. In this study, we show that, in the absence of the BFP retraction ATPase (BfpF), BfpI, BfpJ, and BfpK are dispensable for BFP biogenesis. We also demonstrate that these three minor pilins are incorporated along with bundlin into the BFP filament and contribute to its structural integrity and host cell adhesive properties. The results confirm that previous findings in T4aP systems can be extended to a model T4bP such as BFP.IMPORTANCE Bundle-forming pili contribute to the host colonization strategy of enteropathogenic Escherichia coli. The studies described here investigate the role for three minor pilin subunits in the structure and function of BFP in EPEC. The studies also suggest that these subunits could be antigens for vaccine development.
Highlights
Enteropathogenic Escherichia coli (EPEC) remains a significant cause of infant diarrheal illness and associated morbidity and mortality in developing countries
The results presented in a previous report [19], confirmed in this study, demonstrated that mutant EPEC strains lacking the ability to express BfpI, BfpJ, or BfpK do not produce bundle-forming pili (BFP)
The structural and functional roles of minor pilins have been studied mostly in T4aP systems and just recently in the type 4b pili (T4bP) expressed by enterotoxigenic E. coli [22, 36,37,38]
Summary
Enteropathogenic Escherichia coli (EPEC) remains a significant cause of infant diarrheal illness and associated morbidity and mortality in developing countries. The main virulence feature of the enteropathogenic Escherichia coli (EPEC) group of enterovirulent E. coli is their ability to produce attaching-and-effacing (A/E) lesions on the epithelial lining of the human small intestine [1]. These lesions result from the rearrangement of the actin cytoskeleton, leading to the loss of microvilli and, subsequently, intimate attachment of the organisms to host intestinal epithelial cells [2]. In addition to participating in the early nonintimate phase of EPEC adherence to host intestinal cells, T4aP have been implicated in such processes as immune evasion, twitching motility, biofilm development, autoaggregation, and phage attachment [8,9,10,11,12,13,14]. In addition to bfpA, the gene that encodes bundlin [18], there are three additional genes (bfpI, bfpJ, and bfpK) which encode pilin-like proteins that share many structural features with bundlin, including the prepilin peptidase cleavage site [19], the hydrophobic N-terminal se-
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