Thompson Terissa, Brown Paul D
Pathog Glob Health. 2014 Sep;108(6):283-91. doi: 10.1179/2047773214Y.0000000155. Epub 2014 Oct 16.
This study compared the presence of 35 virulence genes, resistance phenotypes to 11 anti-staphylococcal antibiotics, and pathogenicity in methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA).
Multiplex PCR analysis was used to differentiate Staphylococcus aureus isolates (n = 102) based on characterization of the Staphylococcal Cassette Chromosome mec (SCCmec). Singleplex and multiplex PCR assays targeting 35 virulence determinants were used to analyze the virulence repertoire of S. aureus. In vitro activities of the antibiotics were determined by the disk-diffusion method. The pathogenicity of representative isolates was assessed using Caenorhabditis elegans survival assays. Significance in virulence distribution and antibiotic resistance phenotypes was assessed using the Chi-squared tests. Kaplan-Meier survival estimates were used to analyze nematode survival and significance of survival rates evaluated using the log-rank test.
Except for sei (staphylococcal enterotoxin I) (P = 0·027), all other virulence genes were not significantly associated with MRSA. Resistance to clindamycin (P = 0·03), tetracycline (P = 0·048), trimethoprim/sulfamethoxazole (P = 0·038), and oxacillin (P = 0·004) was significantly associated with MRSA. Survival assay showed MSSA having a lower median lifespan of 3 days than MRSA that had a median lifespan of 6 days. The difference in the killing time of MRSA and MSSA was significant (P < 0·001).
While antibiotic resistance was significantly associated with MRSA, there was no preferential distribution of the virulence genes. The quicker killing potential of MSSA compared to MRSA suggests that carriage of virulence determinants per se does not determine pathogenicity in S. aureus. Pathogenicity is impacted by other factors, possibly antibiotic resistance.
本研究比较了耐甲氧西林金黄色葡萄球菌（MRSA）和甲氧西林敏感金黄色葡萄球菌（MSSA）中35个毒力基因的存在情况、对11种抗葡萄球菌抗生素的耐药表型以及致病性。
采用多重PCR分析基于葡萄球菌盒式染色体mec（SCCmec）的特征区分金黄色葡萄球菌分离株（n = 102）。使用针对35个毒力决定因素的单重和多重PCR检测来分析金黄色葡萄球菌的毒力谱。通过纸片扩散法测定抗生素的体外活性。使用秀丽隐杆线虫存活试验评估代表性分离株的致病性。使用卡方检验评估毒力分布和抗生素耐药表型的显著性。采用Kaplan-Meier生存估计分析线虫存活情况，并使用对数秩检验评估生存率的显著性。
除了sei（葡萄球菌肠毒素I）（P = 0·027）外，所有其他毒力基因与MRSA均无显著相关性。对克林霉素（P = 0·03）、四环素（P = 0·048）、甲氧苄啶/磺胺甲恶唑（P = 0·038）和苯唑西林（P = 0·004）的耐药性与MRSA显著相关。存活试验显示，MSSA的中位寿命为3天，低于MRSA的中位寿命6天。MRSA和MSSA的杀伤时间差异显著（P < 0·001）。
虽然抗生素耐药性与MRSA显著相关，但毒力基因没有优先分布。与MRSA相比，MSSA更快的杀伤潜力表明，毒力决定因素本身的携带并不决定金黄色葡萄球菌的致病性。致病性受其他因素影响，可能是抗生素耐药性。
