Selection of Heterogeneous Vancomycin-Intermediate Staphylococcus aureus by Imipenem
Selection of Heterogeneous Vancomycin-Intermediate Staphylococcus aureus by Imipenem
复制标题
DOI：
10.1128/aac.00834-08
复制
发表时间：
2009-08-01
影响因子：
4.9
通讯作者：
Hiramatsu, Keiichi
中科院分区：
文献类型：
--
作者：
Katayama, Yuki;Murakami-Kuroda, Hiroko;Hiramatsu, Keiichi
万古霉素（货车）中间金黄色葡萄球菌（VISA）和异质性VISA（hVISA）分离株被认为是从VAN敏感的S。金黄色葡萄球菌（VSSA）在货车暴露期间自发突变。我们以前报道，实验室突变H14，从VSSA菌株Delta IP暴露于亚胺培南（IPM），显示过表达的vraSR双组分系统和一个典型的hVISA表型。在本研究中，为了阐明VSSA转化为hVISA的机制，我们通过测定其全基因组序列、形态、细胞壁合成活性和基因表达来进一步表征菌株H14。基因组测序显示，H14携带突变的vraS（命名为vraS（H14）），其引起氨基酸取代（S-329 -> L）。该突变不同于在代表性临床hVISA菌株Mu 3中鉴定的VraS突变（N-5 -> I）。然而，H14表现出与Mu 3相似的表型，包括对货车的异质抗性、增强的细胞壁合成活性和vraSR过表达。用突变的vraS（H14）基因替换Delta IP的vraS基因证实了S-329 -> L取代负责vraSR的上调和向hVISA表型的转化。该转化也通过使用携带突变（N-5 -> I）的Mu 3的vraS基因而不是菌株N315的天然vraS基因来实现。最后，我们进行了一项研究，通过将Delta IP暴露于选择性浓度的货车和β-内酰胺抗生素，分析来自VSSA的hVISA的出现。在货车和IPM筛选的50株分离株中，分别检出8株和5株hVISA。在13个hVISA突变体中，仅在突变株H14中检测到vraSR突变，表明其他突变机制可能是导致hVISA表型进化的原因。我们的结论是，不仅暴露于货车，而且暴露于β-内酰胺类药物可能选择降低S.金黄色。
Vancomycin (VAN)-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA) isolates are considered to have emerged from VAN-susceptible S. aureus (VSSA) by spontaneous mutation during VAN exposure. We previously reported that laboratory mutant H14, obtained from VSSA strain Delta IP by exposure to imipenem (IPM), showed overexpression of the vraSR two-component system and a typical hVISA phenotype. In the present study, to elucidate the mechanism of VSSA conversion to hVISA, we further characterized strain H14 by determining its whole-genome sequence, morphology, cell wall synthetic activity, and gene expression. Genome sequencing revealed that H14 harbored a mutated vraS (designated vraS(H14)) that caused an amino acid substitution (S-329 -> L). This mutation is different from the VraS mutation (N-5 -> I) identified in representative clinical hVISA strain Mu3. However, H14 exhibited a phenotype similar to that of Mu3, including heterogeneous resistance to VAN, enhanced cell wall synthetic activity, and vraSR overexpression. Replacement of the vraS gene of Delta IP with the mutated vraS(H14) gene confirmed that the S-329 -> L substitution was responsible for both the upregulation of vraSR and conversion to the hVISA phenotype. This conversion was also achieved by using the vraS gene of Mu3, which carries a mutation (N-5 -> I), but not with the native vraS gene of strain N315. Finally, we carried out a study to analyze the appearance of hVISA from VSSA by exposure of Delta IP to selective concentrations of VAN and beta-lactam antibiotics. A total of 8 and 5 hVISA isolates were detected among 50 isolates selected with VAN and IPM, respectively. Among the 13 hVISA mutants, mutation in vraSR was detected only in mutant strain H14, suggesting that additional mutational mechanisms can be responsible for evolution to the hVISA phenotype. We conclude that exposure not only to VAN but also to beta-lactams may select for reduced glycopeptide susceptibility in S. aureus.