Methicillin resistance in Staphylococcus aureus requires glycosylated wall teichoic acids

Staphylococcus aureus peptidoglycan (PG) is densely functionalized with anionic polymers called wall teichoic acids (WTAs). These polymers contain three tailoring modifications: D-alanylation, alpha-O-GlcNAcylation, and beta-O-GlcNAcylation. Here we describe the discovery and biochemical characterization of a unique glycosyltransferase, TarS, that attaches beta-O-GlcNAc (beta-O-N-acetyl-D-glucosamine) residues to S. aureus WTAs. We report that methicillin resistant S. aureus (MRSA) is sensitized to beta-lactams upon tarS deletion. Unlike strains completely lacking WTAs, which are also sensitive to beta-lactams, Delta tarS strains have no growth or cell division defects. Because neither alpha-O-GlcNAc nor beta-O-Glucose modifications can confer resistance, the resistance phenotype requires a highly specific chemical modification of the WTA backbone, beta-O-GlcNAc residues. These data suggest beta-O-GlcNAcylated WTAs scaffold factors required for MRSA resistance. The beta-O-GlcNAc transferase identified here, TarS, is a unique target for antimicrobials that sensitize MRSA to beta-lactams.