Shopsin B, Mathema B, Zhao X, Martinez J, Kornblum J, Kreiswirth B N
Public Health Research Institute, New York, NY 10016, USA.
Microb Drug Resist. 2000 Fall;6(3):239-44. doi: 10.1089/mdr.2000.6.239.
The population structure of methicillin-resistant Staphylococcus aureus (MRSA) is predominantly clonal, which may be related to the fitness of the genetic background of the methicillin-susceptible S. aureus (MSSA) into which the mecA chromosomal resistant determinant has inserted. To test this idea, we assessed whether the genotypes of New York MRSA are present in MSSA populations by using a combination of protein A gene sequence typing (spa typing) and pulsed-field gel electrophoresis (PFGE). Although about 16% of colonizing MSSA isolated from community subjects were related to MRSA, only one of the five predominant New York MRSA clonal types was found among the MSSA isolates. Similarly, among nosocomial MSSA, only four MRSA homologues were observed, two of which may have arisen through deletion of the mec element. Thus, MRSA clonal types represent a limited spectrum of the diversity seen in community and hospital S. aureus populations. The data are best explained by antibiotic selection pressure, as opposed to increased transmissibility or virulence, being responsible for the clonal dissemination of the resistance phenotype in MRSA genetic backgrounds, an in turn, the limited spread of these strains outside of the hospital environment.
耐甲氧西林金黄色葡萄球菌（MRSA）的种群结构主要是克隆性的，这可能与mecA染色体抗性决定簇插入其中的甲氧西林敏感金黄色葡萄球菌（MSSA）遗传背景的适应性有关。为了验证这一想法，我们通过结合蛋白A基因序列分型（spa分型）和脉冲场凝胶电泳（PFGE）来评估纽约MRSA的基因型是否存在于MSSA种群中。尽管从社区受试者中分离出的约16%的定植MSSA与MRSA有关，但在MSSA分离株中仅发现了五种主要纽约MRSA克隆类型中的一种。同样，在医院获得性MSSA中，仅观察到四种MRSA同源物，其中两种可能是通过mec元件的缺失产生的。因此，MRSA克隆类型代表了社区和医院金黄色葡萄球菌种群中所见多样性的有限范围。这些数据最好用抗生素选择压力来解释，而不是增加的传播性或毒力，抗生素选择压力导致了MRSA遗传背景中抗性表型的克隆传播，进而导致这些菌株在医院环境之外的有限传播。
