Multidrug Resistance in Staphylococcus aureus Due to Overexpression of a Novel Multidrug and Toxin Extrusion (MATE) Transport Protein

Abstract

Efflux is an important mechanism of multidrug resistance (MDR) in bacteria. The multidrug and toxin extrusion (MATE) family is the most recently described group of MDR efflux proteins, none of which have previously been identified in Staphylococcus aureus. Two independently derived S. aureus mutants having efflux-related MDR phenotypes were studied using microarray technology and a marked overexpression of an open reading frame (ORF; mepA) encoding a protein homologous with MATE family proteins was observed in both. There was concomitant overexpression of ORFs in close proximity to mepA (ϳ100 bp) encoding a MarR-type regulator (mepR, upstream of mepA) and a protein of unknown function (mepB, downstream). Experiments in which mepA was overexpressed or disrupted revealed that the encoded protein has a broad substrate profile that includes several monovalent and divalent biocides and the fluoroquinolone antimicrobial agents norfloxacin and ciprofloxacin. The function of MepB is obscure, it does not contribute to the MDR phenotype conferred by MepA. MepR overexpression reversed the MDR phenotypes of both mutants by repressing mepA transcription. All three ORFs are preferentially transcribed as a single mepRAB unit, suggesting that the three genes form an operon.

Characterization of the MSMEG_2631 Gene ( mmp ) Encoding a Multidrug and Toxic Compound Extrusion (MATE) Family Protein in Mycobacterium smegmatis and Exploration of Its Polyspecific Nature Using Biolog Phenotype MicroArray

“…The norM promoter is induced at 18°C in Erwinia amylovora (61), DNA-damaging compounds induce dinF in Clostridium difficile (62) and R. solanacearum (58), and mepR negatively regulates S. aureus mepB MATE transcription (24). Our data indicate that MSMEG_2626-2628-2629-2630-2631 operon transcription is initiated from a single TSS and suggest that the promoter is constitutive, since no tested drugs induce promoter activity.…”

“…In E. coli and Streptococcus pneumoniae, dinF is in operons with lexA and recA, respectively (56,57). In Staphylococcus aureus, the mepRAB operon encodes a MarR-like transcriptional regulator (mepR), a MATE family efflux pump (mepA), and a hypothetical protein (mepB) (24). In Ralstonia solanacearum, dinF is flanked by genes encoding a hypothetical amino acid permease and a putative transmembrane protein (58).…”

“…Efflux pumps can contribute to acquired drug resistance due to overexpression (24,49) and to MDR (24,50,51). Drug efflux families, the MATE family being the most recently added group (18), have been studied for function and physiological importance (52).…”

“…The genomic organization of MATE efflux pump gene flanking regions has been studied in DinFs in several bacteria (24,(56)(57)(58). In E. coli and Streptococcus pneumoniae, dinF is in operons with lexA and recA, respectively (56,57).…”

“…In plants, MATE transporters secrete secondary metabolites to defend against microbial pathogens (20,21), and in the liver and kidney they extrude xenobiotic cations (22,23). Bacterial MATE transporters function as xenobiotic efflux pumps and can confer resistance to structurally diverse drugs, including antibiotics and DNA-damaging agents (24,25).…”