Mutations inmmpLand in the Cell Wall Stress Stimulon Contribute to Resistance to Oxadiazole Antibiotics in Methicillin-Resistant Staphylococcus aureus
ABSTRACTStaphylococcus aureusis a leading cause of hospital- and community-acquired infections, which exhibit broad resistance to various antibiotics. We recently disclosed the discovery of the oxadiazole class of antibiotics, which hasin vitroandin vivoactivities against methicillin-resistantS. aureus(MRSA). We report herein that MmpL, a putative member of the resistance, nodulation, and cell division (RND) family of proteins, contributes to oxadiazole resistance in theS. aureusstrain COL. Through serial passages, we generated twoS. aureusCOL variants that showed diminished susceptibilities to an oxadiazole antibiotic. The MICs for the oxadiazole against one strain (designatedS. aureusCOLI) increased reproducibly 2-fold (to 4 μg/ml), while against the other strain (S. aureusCOLR), they increased >4-fold (to >8 μg/ml, the limit of solubility). The COLRstrain was derived from the COLIstrain. Whole-genome sequencing revealed 31 mutations inS. aureusCOLR, of which 29 were shared with COLI. Consistent with our previous finding that oxadiazole antibiotics inhibit cell wall biosynthesis, we found 13 mutations that occurred either in structural genes or in promoters of the genes of the cell wall stress stimulon. Two unique mutations inS. aureusCOLRwere substitutions in two genes that encode the putative thioredoxin (SACOL1794) and MmpL (SACOL2566). A role formmpLin resistance to oxadiazoles was discerned from gene deletion and complementation experiments. To our knowledge, this is the first report that a cell wall-acting antibiotic selects for mutations in the cell wall stress stimulon and the first to implicate MmpL in resistance to antibiotics inS. aureus.