Bundle-Forming Pili and EspA Are Involved in Biofilm Formation by EnteropathogenicEscherichia coli

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Abstract
Microcolony formation is one of the initial steps in biofilm development, and in enteropathogenicEscherichia coli(EPEC) it is mediated by several adhesins, including the bundle-forming pilus (BFP) and the EspA filament. Here we report that EPEC forms biofilms on plastic under static conditions and a flowthrough continuous culture system. The abilities of several EPEC isogenic mutants to form biofilms were assessed. Adhesins such as BFP and EspA, important in microcolony formation on epithelial cells, are also involved in bacterial aggregation during biofilm formation on abiotic surfaces. Mutants that do not express BFP or EspA form more-diffuse biofilms than does the wild type. We also determined, usinggfptranscriptional fusions, that, consistent with the role of these adhesins in biofilms, the genes encoding BFP and EspA are expressed during biofilm formation. Finally, expression ofespAis controlled by a quorum-sensing (QS) regulatory mechanism, and the EPECqseAQS mutant also forms altered biofilms, suggesting that this signaling mechanism plays an important role in EPEC biofilm development. Taken together, these studies allowed us to propose a model of EPEC biofilm formation.