The Major Pilin Subunit of the AAF/II Fimbriae from Enteroaggregative Escherichia coli Mediates Binding to Extracellular Matrix Proteins

Enteroaggregative Escherichia coli (EAEC) adherence to human intestinal tissue is mediated by aggregative adherence fimbriae (AAF); however, the receptors involved in EAEC adherence remain uncharacterized. Adhesion to extracellular matrix proteins is commonly observed among enteric pathogens, so we addressed the hypothesis that EAEC may bind to extracellular matrix proteins commonly found in the intestine. We found that EAEC prototype strain 042 adhered more abundantly to surfaces that were precoated with the extracellular matrix proteins fibronectin, laminin, and type IV collagen. Differences in fibronectin binding of almost 2 orders of magnitude were observed between EAEC 042 and a mutant in the AAF/II major pilin gene, aafA. Purified AafA, refolded as a donor strand complementation construct, bound fibronectin in a dose-dependent manner. Addition of fibronectin to the apical surfaces of polarized T84 cell monolayers augmented EAEC 042 adherence, and this effect required expression of aafA. Finally, increased bacterial adherence was observed when apical secretion of fibronectin was induced by adenosine in polarized T84 cells. Binding to fibronectin may contribute to colonization of the gastrointestinal tract by EAEC.