Deciphering the role of multidrug efflux pumps in the virulence of enteroaggregative Escherichia coli

Efflux pumps (EPs) constitute an important group of membrane proteins that characterize all living organisms, from bacteria to humans. Acting as intermembrane transporters, they perform a crucial role in the extrusion of different types of compounds from the cell, and their overexpression constitutes one of the main mechanisms employed by bacteria to implement multidrug resistance (MDR). Although MDR EPs are mainly involved in antibiotic excretion mechanisms, many other functions have been attributed to them including communication with the external environment and host cell, stress response, and biofilm formation. Despite their relevance in many pathogens, up to now no data are available on the potential role of MDR EPs during the pathogenicity process of enteroaggregative Escherichia coli (EAEC). EAEC is a group of enteropathogenic E. coli that are known for their ability to form thick biofilms on the intestinal mucosa and represents the leading cause of acute and persistent diarrhoea worldwide. Using the clinical strain EAEC 17-2 as a model, we first identified in silico the genetic loci encoding MDR EPs. Then, by site-specific mutagenesis, we isolated mutants in genes encoding MDR EPs known to be involved in biofilm biogenesis in commensal E. coli. Preliminary results indicated that AcrAB, the major MDR EP, is implicated in biofilm formation and maturation as the loss of the AcrB transporter leads to a significant reduction of extracellular DNA in the biofilm matrix.