Investigation of the potential association between a novel autotransporter adhesin (Ema: extracelular matrix-binding autotransporter) and the aggregative adherence fimbriae II (AAF/II) on biofilm formation by enteroaggregative Escherichia coli isolates.

Abstract

Biofilm formation is a key virulence factor for the pathogenesis of many bacteria, allowing them to adhere in distinct surfaces, escape from antimicrobial drugs and evade the host's immune system. Biofilm formation depends on several factors, among which the adhesins are considered essential for pathogen attachment to biotic and abiotic surfaces. Among the pathogens that form biofilm, we can highlight the Enteroaggregative Escherichia coli (EAEC). EAEC is a pathogen that causes acute or persistent diarrhea affecting both children and adults. EAEC is characterized by forming the aggregative adherence pattern (AA) in which the bacterial cells associate one another in an arrangement that resembles stacked bricks in adhesion assays performed with epithelial cells (HeLa or Hep-2). The AA pattern formation is mediated by the aggregative adherence fimbriae (AAFs), and, so far, five distinct variants are known (AAF/I, AAF/II, AAF/III, AAF/IV and AAF/V); moreover, these fimbriae are closely related to the formation of biofilm in EAEC isolates. Very recently, our research group identified a novel autotransporter protein termed Extracelular Matrix-binding Autotransporter (Ema), which participates in several adhesion phenotypes, including biofilm formation. Considering that biofilm formation is a multifactorial phenotype, a study carried out by our research group investigated the role of Ema in the biofilm formation of multiple EAEC isolates harboring genes responsible for encoding proteins associated with the biogenesis of the five AAF variants. Surprisingly, Ema increased biofilm formation only in an EAEC isolate (P184-1) that harbored genes responsible for encoding the proteins that synthesize AAF/II. Despite this result, so far, we can not conclude that this increase in the ability to form biofilm, observed in the isolate P184-1 is, in fact, due to the synergistic association between Ema and AAF/II. Thus, the present study aims to clarify the existence of a possible synergistic association between Ema and AAF/II in EAEC isolates during biofilm formation.