Disruption of the <i>tagF</i> Orthologue in the <i>epa</i> Locus Variable Region of Enterococcus faecalis Causes Cell Surface Changes and Suppresses an <i>eep</i>-Dependent Lysozyme Resistance Phenotype.

The disease-producing capacity of the opportunistic pathogen Enterococcus faecalis is enhanced by the ability of the bacterium to evade killing by antimicrobial agents. Survival of E. faecalis in the presence of the human antimicrobial enzyme lysozyme is mediated in part by the site 2 metalloprotease Eep; however, a complete model of enterococcal lysozyme resistance has not been elucidated. To better understand the molecular basis for lysozyme resistance in E. faecalis, we analyzed Δ<i>eep</i> suppressor mutants that acquire resistance to lysozyme through mutation of the gene <i>OG1RF_11713</i>, a predicted teichoic acid biosynthesis-encoding gene located within the variable region of the enterococcal polysaccharide antigen (<i>epa</i>) locus. Sequence comparisons revealed that <i>OG1RF_11713</i> is most similar to the cytidine-5'-diphosphate (CDP)-glycerol:poly-(glycerolphosphate)glycerophosphotransferase TagF from Staphylococcus epidermidis. Inactivation of <i>OG1RF_11713</i> in both the wild-type and Δ<i>eep</i> genetic backgrounds was sufficient to increase the resistance of E. faecalis OG1RF to lysozyme. Minimal amounts of <i>N</i>-acetylgalactosamine were detectable in cell wall carbohydrate extracts of <i>OG1RF_11713</i> deletion mutants, and this was associated with a reduction in negative cell surface charge. Targeted disruption of <i>OG1RF_11713</i> was also associated with increased susceptibility to the antibiotic polymyxin B and membrane-targeting detergents and decreased susceptibility to the lantibiotic nisin. This work implicates <i>OG1RF_11713</i> as a major determinant of cell envelope integrity and provides further validation that lysozyme resistance is intrinsically linked to the modification of enterococcal cell wall polysaccharides. <b>IMPORTANCE</b> Enterococcus faecalis is a leading cause of health-care-associated infections for which there are limited treatment options. E. faecalis is resistant to several antibiotics and to high concentrations of the human antimicrobial enzyme lysozyme. The molecular mechanisms that mediate lysozyme resistance in E. faecalis are complex and remain incompletely characterized. This work demonstrates that a gene located within the variable region of the enterococcal polysaccharide antigen locus of E. faecalis strain OG1RF (<i>OG1RF_11713</i>), which is predicted to encode a component of the teichoic acid biosynthesis machinery, is part of the lysozyme resistance circuitry and is important for enterococcal cell wall integrity. These findings suggest that <i>OG1RF_11713</i> is a potential target for new therapeutic strategies to combat enterococcal infections.