中文摘要：

目的探讨金黄色葡萄球菌XQ株毒力变异的机制。方法以金黄色葡萄球菌ATCC25923为对照,采用动物实验观察临床分离的金葡菌XQ株在体外传代后的毒力改变;通过聚丙烯酰胺凝胶电泳（SDS-PAGE）分析菌体及培养上清的蛋白谱变化,应用PCR进行金葡菌附属调节基因agr扩增并测序,分析菌株毒力变异的机制,并进一步通过qRT-PCR检测XQ株agr调控的毒力因子变化情况。结果动物毒力实验证实XQ株的毒力较对照菌ATCC25923强,体外传代培养后,XQ株第180代菌株（XQ180）的毒力明显下降,SDS-PAGE分析发现毒力下降的XQ株（XQM株）培养上清的蛋白表达谱较XQ株有明显改变,对金葡菌agr基因进行测序分析发现XQM株的agr C基因第443位有一段188 bp的序列插入,而该插入序列就是agr C基因255~442间序列,正是该188 bp重复序列导致Agr C蛋白的截短型突变,引起新桥株的致病性降低,qRT-PCR检测结果证实XQM株中受agr调控的毒力基因表达水平显著下降。结论临床分离的金葡菌XQ株毒力强,在体外传代中易发生毒力变异,这种变异与重复序列导致的agr C突变有关。

英文摘要：

Objective To investigate the underlying mechanism of variable virulence in Staphylococcus aureus strain XQ. Methods After subculturing in vitro,the virulence change in clinical isolated stain XQ of Staphylococcus aureus（ S. aureus） was tested in BALB / c mouse models,and S. aureus strain ATCC25923 was used as control. Protein expression profiles in bacterial cells and supernatants were determined by SDS-PAGE analysis. The genes of accessory gene regulator（ agr） were amplified by PCR and then sequenced,and the expression levels of virulence factor genes controlled by agr in XQ and XQM were also determined by quantitative real-time reverse transcription PCR（ qRT-PCR）. Results S. aureus XQ strain was more virulent than ATCC25923,however,after culturing in vitro,the virulence of the 180 th generation of XQ strain（ XQ180） was significantly decreased,and SDS-PAGE analysis demonstrated that the protein expression patterns in the culture supernatants were different between XQ and the virulence attenuated strain（ XQM）. The sequencing results indicated an extra 188 bp repeated sequence was inserted into the443 th of nucleotide agr C gene,resulting in a truncated mutant of Agr C protein. What ＇s more,the gene expression levels controlled by agr were markedly reduced in XQMstrain. Conclusion XQ is a highvirulence strain of S. aureus,and prone to virulence variation during cultured in vitro. The virulence variation of S. aureus XQ is associated with the agr C mutant caused by a repeated sequence insertion.