Multiple Roles for Enterococcus faecalis Glycosyltransferases in Biofilm-Associated Antibiotic Resistance, Cell Envelope Integrity, and Conjugative Transfer

Abstract

ABSTRACTThe emergence of multidrug-resistant bacteria and the limited availability of new antibiotics are of increasing clinical concern. A compounding factor is the ability of microorganisms to form biofilms (communities of cells encased in a protective extracellular matrix) that are intrinsically resistant to antibiotics.Enterococcus faecalisis an opportunistic pathogen that readily forms biofilms and also has the propensity to acquire resistance determinants via horizontal gene transfer. There is intense interest in the genetic basis for intrinsic and acquired antibiotic resistance inE. faecalis, since clinical isolates exhibiting resistance to multiple antibiotics are not uncommon. We performed a genetic screen using a library of transposon (Tn) mutants to identifyE. faecalisbiofilm-associated antibiotic resistance determinants. Five Tn mutants formed wild-type biofilms in the absence of antibiotics but produced decreased biofilm biomass in the presence of antibiotic concentrations that were subinhibitory to the parent strain. Genetic determinants responsible for biofilm-associated antibiotic resistance include components of the quorum-sensing system (fsrA,fsrC, andgelE) and two glycosyltransferase (GTF) genes (epaIandepaOX). We also found that the GTFs play additional roles inE. faecalisresistance to detergent and bile salts, maintenance of cell envelope integrity, determination of cell shape, polysaccharide composition, and conjugative transfer of the pheromone-inducible plasmid pCF10. TheepaOXgene is located in a variable extended region of the enterococcal polysaccharide antigen (epa) locus. These data illustrate the importance of GTFs inE. faecalisadaptation to diverse growth conditions and suggest new targets for antimicrobial design.