Objective: To investigate the mechanisms by which MecA gene expression leads to β-lactam resistance in methicillin-resistant Staphylococcus aureus (MRSA), and to study the resistance mechanism of MRSA at the molecular level.Methods: A variety of molecular biological techniques were employed, including screening MRSA using cefoxitin paper disk method, extraction of MRSA mRNA, reverse transcription into cDNA, real-time fluorescence PCR for quantitation of MecA gene expression, and agar dilution method for assessment of minimum inhibitory concentrations in MRSA treated with cefoxitin, oxacillin, vancomycin, or linezolid.Results: According to the level of resistance of MRSA to cefoxitin, 40 MRSA strains were divided into a low resistance group (n=12), a middle resistance group (n=15), and a high resistance group (n=13). The expression level of the MecA gene in the low resistance group, the middle resistance group, and the high resistance group was 58.87±30.30, 363.37±200.05, and 1257.72±446.63,respectively. MRSA resistance to cefoxitin and oxacillin was 100%; MRSA resistance to vancomycin or linezolid could not be detected. For all 40 MRSA strains the MIC90 for vancomycin was 2.0 μg/mL. Conclusion: MecA gene expression levels may correlate with the MRSA level of resistance to cefoxitin within a certain range of concentration.%目的:探讨耐甲氧西林金黄色葡萄球菌(MRSA)中MecA基因表达水平对β-内酰胺类抗生素耐药的机制与作用.方法:利用头孢两丁纸片法筛选MRSA,提取MRSA细菌RNA,反转录成cDNA,实时荧光PCR检测MecA基因的表达水平；琼脂稀释法检测MRSA对头孢西丁、苯唑西林、万古霉素、利奈唑胺的最低抑菌浓度.结果:40株MRSA分为低水平耐药组(12株)、中水平耐药组(15株)、高水平耐药组(13株).MecA基因的表达水平在MRSA低水平耐药组、中水平耐药组、高水平耐药组分别为58.87±30.30,363.37±200.05,1257.72±446.63,MRSA对头孢西丁、苯唑西林的耐药率为100.0％,没有检测到对万古霉素、利奈唑胺耐药的MRSA,但40株MRSA万古霉素的90％的细菌被抑制的浓度(MIC90)为2.0μG/ML.结论:MecA基因的表达水平可能与MRSA对β-内酰胺类抗生素耐药程度相关.
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