Goldstein Fred, Perutka Jiri, Cuirolo Arabela, Plata Konrad, Faccone Diego, Morris Joanne, Sournia Aude, Kitzis Marie Dominique, Ly Aicha, Archer Gordon, Rosato Adriana E
Division of Infectious Diseases, Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA 23298, USA.
Antimicrob Agents Chemother. 2007 Jul;51(7):2514-22. doi: 10.1128/AAC.00040-07. Epub 2007 Apr 30.
Methicillin resistance in Staphylococcus aureus is primarily mediated by the acquired penicillin-binding protein PBP 2a, which is encoded by mecA. PBP 2a acts together with native PBP 2 to mediate oxacillin resistance by contributing complementary transpeptidase and transglycosylase activities, respectively. In this study, we have investigated a phenotype of beta-lactam dependence in a clinical methicillin-resistant S. aureus strain (strain 2884D) obtained by in vitro selection with ceftobiprole. 28884D, which grew very poorly in blood agar, required the presence of the beta-lactam antibiotics to grow. On the basis of this observation, we hypothesized that a gene or genes essential for growth were dependent on oxacillin induction. Identification and analysis of genes regulated by oxacillin were performed by both real-time reverse transcription-PCR and spotted microarray analysis. We found that mecA was constitutively expressed in strain 2884D and that the constitutive expression resulted from perturbations in the two systems involved in its regulation, i.e., MecI/MecR1 (staphylococcal chromosome cassette mec type I) and BlaI/BlaR1 (nonfunctional penicillinase operon). PBP 2 appeared to be poorly induced by oxacillin in 2884D. Further analysis of the PBP 2 two-component VraSR regulatory system showed that it was nonfunctional, accounting for the lack of response to oxacillin. Together, these results support the notion that limited PBP 2 availability may have led 2884D to become dependent on oxacillin-mediated mecA induction as a required survival mechanism.
金黄色葡萄球菌对甲氧西林的耐药性主要由获得性青霉素结合蛋白PBP 2a介导，该蛋白由mecA编码。PBP 2a与天然PBP 2共同作用，分别通过提供互补的转肽酶和转糖基酶活性来介导对苯唑西林的耐药性。在本研究中，我们调查了一株通过头孢比普体外筛选获得的临床耐甲氧西林金黄色葡萄球菌菌株（2884D株）的β-内酰胺依赖性表型。2884D在血琼脂中生长非常差，需要β-内酰胺类抗生素的存在才能生长。基于这一观察结果，我们推测一个或多个生长必需基因依赖于苯唑西林诱导。通过实时逆转录PCR和斑点微阵列分析对受苯唑西林调控的基因进行了鉴定和分析。我们发现mecA在2884D株中组成性表达，这种组成性表达是由其调控所涉及的两个系统，即MecI/MecR1（葡萄球菌盒式染色体mec I型）和BlaI/BlaR1（无功能青霉素酶操纵子）的扰动导致的。在2884D中，PBP 2似乎很少被苯唑西林诱导。对PBP 2双组分VraSR调控系统的进一步分析表明它无功能，这解释了对苯唑西林缺乏反应的原因。总之，这些结果支持了这样一种观点，即有限的PBP 2可用性可能导致2884D依赖于苯唑西林介导的mecA诱导作为一种必需的生存机制。
