Boyle-Vavra Susan, Yin Shaohui, Daum Robert S
Department of Pediatrics Section of Pediatric Infectious Diseases, The University of Chicago, Chicago, IL 60637, USA.
FEMS Microbiol Lett. 2006 Sep;262(2):163-71. doi: 10.1111/j.1574-6968.2006.00384.x.
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.
金黄色葡萄球菌对甲氧西林/苯唑西林（Oxa）的耐药性主要由mecA编码的获得性青霉素结合蛋白（PBP2a）介导。PBP2a分别通过贡献互补的转肽酶和转糖基酶活性，与天然PBP2共同作用以介导苯唑西林耐药性。VraS/VraR双组分调节系统可被细胞壁抗菌药物（β-内酰胺类、糖肽类）诱导，并控制包括pbp2及其自身在内的许多细胞壁基因的转录诱导。我们通过使社区获得性耐甲氧西林金黄色葡萄球菌临床分离株中的vraS失活，研究了VraS/VraR在苯唑西林耐药性表型表达中的作用，这些分离株缺乏编码mecA调节序列mecI和mecR1的功能基因。vraS失活消除了苯唑西林耐药性，用vraS操纵子进行互补恢复了耐药表型。vraS突变体中mecA转录增加；然而，PBP2a丰度与野生型相似。虽然vraS突变体中pbp2转录减少，但pbp2操纵子的过表达并未恢复耐药性。这些数据表明，虽然mecA和pbp2的表达是苯唑西林耐药性所必需的，但它们并不充分。因此，vraS/vraR调节系统在允许耐甲氧西林金黄色葡萄球菌通过调节除已知甲氧西林耐药效应子以外的基因靶点来响应β-内酰胺类药物方面起着关键作用。
