title: The VraS/VraR two-component regulatory system required for oxacillin resistance in community-acquired methicillin-resistant Staphylococcus aureus.
abstract: Methicillin/oxacillin (Oxa) resistance in Staphylococcus aureus is primarily mediated by the acquired penicillin-binding protein (PBP2a) encoded by mecA. PBP2a acts together with native PBP2 to mediate oxacillin resistance by contributing complementary transpeptidase and transglycosylase activities, respectively. The VraS/VraR two-component regulatory system is inducible by cell-wall antimicrobials (beta-lactams, glycopeptides) and controls transcriptional induction of many cell-wall genes including pbp2 and itself. We investigated the role of VraS/VraR in the phenotypic expression of oxacillin resistance by inactivating vraS in community-acquired MRSA clinical isolates that lack functional genes encoding the mecA regulatory sequences mecI and mecR1. Inactivation of vraS abrogated oxacillin resistance, and complementation with the vraS operon restored the resistance phenotype. mecA transcription increased in the vraS mutants; however, PBP2a abundance was similar to that of the wild type. Although pbp2 transcription decreased in the vraS mutants, overexpression of the pbp2 operon did not restore resistance. These data demonstrate that although expressions of mecA and pbp2 are required for oxacillin resistance, they are not sufficient. Therefore, the vraS/vraR regulatory system plays a crucial role in allowing MRSA to respond to beta-lactams by regulation of a gene target other than the known effectors of methicillin resistance.
authors.affiliation: Department of Pediatrics Section of Pediatric Infectious Diseases, The University of Chicago, Chicago, IL 60637, USA. sboyle@peds.bsd.uchicago.edu
authors.forename: Susan
authors.initials: S
authors.lastname: Boyle-Vavra
authors.forename: Shaohui
authors.initials: S
authors.lastname: Yin
authors.forename: Robert S
authors.initials: RS
authors.lastname: Daum
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D015152:Blotting, Northern; D015153:Blotting, Western; D002876:Chromosomes, Bacterial / Q000235:genetics; D017714:Community-Acquired Infections / Q000382:microbiology; D004268:DNA-Binding Proteins; D005816:Genetic Complementation Test; D006801:Humans; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009876:Operon; D010068:Oxacillin / Q000494:pharmacology*; D046915:Penicillin-Binding Proteins / Q000096:biosynthesis; D010453:Peptide Synthases / Q000096:biosynthesis; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D046915:Penicillin-Binding Proteins; C478170:VraR protein, Staphylococcus aureus; C478169:VraS protein, Staphylococcus aureus; C478699:penicillin-binding protein 2a, Streptococcus; D010453:Peptide Synthases; D010068:Oxacillin