聚合酶链反应检测mecA和mecI及其对葡萄球菌甲氧西林耐药的影响

Detection of mecA and mecI by PCR and effect of mecA and mecI on methicillin resistance of staphylococci

目的了解葡萄球菌甲氧西林耐药基因mecA和调节基因mecR中的抑制基因mecI在葡萄球菌中的分布,探讨mecA、mecI和β-内酰胺酶对甲氧西林耐药性的影响。方法琼脂稀释法测定158株葡萄球菌苯唑西林MIC;聚合酶链反应检测mecA和mecI;用内切酶TrulⅠ进行mecI酶切分型。结果 158株葡萄球菌中,金黄色葡萄球菌(SA)66株,凝固酶阴性葡萄球菌(CNS)92株,葡萄球菌对苯唑西林的总耐药率达44.3%(70/158)。158株葡萄球菌中,检出mecA阳性70株,其中SA 8株,CNS 62株。70株mecA阳性葡萄球菌中,检出mecI阳性12株,其中SA7株,CNS 5株;88株mecA阴性葡萄球菌中未检出mecI。对mecA阴性、苯唑西林MIC≥4μg/mL的菌株进行抑制实验后,再测定苯唑西林MIC,抑制后MIC下降8倍以上。结论耐甲氧西林葡萄球菌以mecA为其主要的甲氧西林耐药决定子;β-内酰胺酶和mecI基因对葡萄球菌甲氧西林耐药有一定的影响。

Objective To investigate the distribution of mecA,mecI and effect of β-lactamase,mecI on methicillin resistance in Staphylococci.Methods Oxacillin MICs were determined by agar dilution test in 158 staphylococci,mecA and mecI were amplified by PCR,RFLP analysis of mecI was performed by using restriction endonuclease TrulⅠ.Results 158 staphylococci were collected,including 66 Staphylococcus aureus（SA）and 92 coagulase-negative staphylococci（CNS）.The total resistant rate of oxacillin amounted to 44.3%（70/158）.70 of 158 isolates were mecA positive,including 8 SA and 62 CNS.Among 70 mecA positive isolates,12 mecI positive staphylococci were detected,including 7 SA and 5 CNS.Among mecA negative staphylococci,mecI gene was not found.The staphylococci with oxacillin MIC≥4 μg/mL but without mecA were inhibited by clavulanic acid（5 μg/mL）and the oxacillin MIC decreased 8-fold.Conclusion mecA could be the resistant determinant of methicillin resistant staphylococci.β-lactamse and mecI might have effect on methicillin resistance of SA and CNS.