Centre for Infection, Division of Clinical Sciences, St George's, University of London, London, UK.
BMC Microbiol. 2012 Jun 12;12:104. doi: 10.1186/1471-2180-12-104.
Staphylococcus aureus is major human and animal pathogen. Plasmids often carry resistance genes and virulence genes that can disseminate through S. aureus populations by horizontal gene transfer (HGT) mechanisms. Sequences of S. aureus plasmids in the public domain and data from multi-strain microarrays were analysed to investigate (i) the distribution of resistance genes and virulence genes on S. aureus plasmids, and (ii) the distribution of plasmids between S. aureus lineages.
A total of 21 plasmid rep gene families, of which 13 were novel to this study, were characterised using a previously proposed classification system. 243 sequenced plasmids were assigned to 39 plasmid groups that each possessed a unique combination of rep genes. We show some resistance genes (including ermC and cat) and virulence genes (including entA, entG, entJ, entP) were associated with specific plasmid groups suggesting there are genetic pressures preventing recombination of these genes into novel plasmid groups. Whole genome microarray analysis revealed that plasmid rep, resistance and virulence genes were associated with S. aureus lineages, suggesting restriction-modification (RM) barriers to HGT of plasmids between strains exist. Conjugation transfer (tra) complex genes were rare.
This study argues that genetic pressures are restraining the spread of resistance and virulence genes amongst S. aureus plasmids, and amongst S. aureus populations, delaying the emergence of fully virulent and resistant strains.
金黄色葡萄球菌是主要的人类和动物病原体。质粒通常携带耐药基因和毒力基因，可通过水平基因转移（HGT）机制在金黄色葡萄球菌群体中传播。本研究分析了公共领域中金黄色葡萄球菌质粒的序列和多菌株微阵列的数据，以调查：（i）耐药基因和毒力基因在金黄色葡萄球菌质粒上的分布；（ii）质粒在金黄色葡萄球菌谱系之间的分布。
使用先前提出的分类系统，对 21 个质粒 rep 基因家族进行了特征描述，其中 13 个是本研究中首次发现的。243 个测序质粒被分配到 39 个质粒组，每个质粒组都具有独特的 rep 基因组合。我们发现一些耐药基因（包括 ermC 和 cat）和毒力基因（包括 entA、entG、entJ、entP）与特定的质粒组相关，这表明存在遗传压力，阻止这些基因重组到新的质粒组中。全基因组微阵列分析表明，质粒 rep、耐药和毒力基因与金黄色葡萄球菌谱系相关，表明菌株之间的质粒 HGT 存在限制修饰（RM）障碍。接合转移（tra）复合物基因很少见。
本研究认为，遗传压力限制了耐药基因和毒力基因在金黄色葡萄球菌质粒之间以及金黄色葡萄球菌群体中的传播，从而延缓了完全毒力和耐药菌株的出现。
