金黄色葡萄球菌耐药机制的研究

目的探讨金黄色葡萄球菌的耐药性及耐药机制。方法按NCCLS推荐的琼脂平皿对倍稀释法测定分离鉴定的198株金黄色葡萄球菌对苯唑西林的耐药性（MIC值）；用Nitroeephin纸片法测定各菌株产酶情况，统计对苯唑西林不同耐药水平的金黄色葡萄球菌产酶率并分析其耐药水平和产酶率的相关关系；PCR测定各菌株含mecA基因情况。结果198株金黄色葡萄球菌对苯唑西林的耐药率为64．65％;128株耐甲氧西林金黄色葡萄球菌（MRSA）中，高耐菌株为118株（92．19oA），低耐株为10株（7．81%）。敏感株产酶率为58．57％（41株），高耐株产酶率53．39％（63株），低耐株产酶率40．00％（4株），苯唑西林敏感株与高耐株之间产β-内酰胺酶的差别有统计学意义，前者高于后者；含mecA基因的高耐株占95．76％（113／118）、低耐株占60．00％（6／10）、敏感株占10．00％（7／70），高耐株与敏感株含mecA基因的差别有统计学意义，前者高于后者。结论金黄色葡萄球菌耐药机制主要是产β-内酰胺酶和mecA基因的表达。

A Study on the Mechanism of Drug Resistance in Staphylococcus aureus

OBJECTIVE: To inquire into the mechanism of drug resistance in Staphylococcus aureus. METHODS: A total of 198 strains of Staphylococcus aureus were isolated from the samples sent to the Clinical Laboratory of Microbiology,West China Hospital. The resistance of Staphylococcus aureus to Methicillin was assayed with agar dilution. Staphylococcus aureus mecA gene was measured by PCR assay and beta-lactamase was detected by Nitrocephin. RESULTS: The rate of resistance to methicillin was 64.65% in 198 strains of Staphylococcus aureus; 118 strains of methicillin-resistant staphylococcus aureus(MRSA) were found to have high level resistance in 128 MRSA;10 strains of MRSA were found to have low level resistance; 41(58.57%) strains of methicillin-sensitive Staphylococcus aureus (MSSA) expressed beta-lactamase; 2 Staphylococcus aureus had mecA among them; 67 Staphylococcus aureus expressed beta-lactamase in high level resistance, 63(53.39%)Staphylococcus aureus expressed beta-lactamase in high level resistance, among them, 5 Staphylococcus aureus had mecA; 40.00% MRSA expressed beta-lactamase in low level resistance, 55 MRSA did not express beta-lactamase in high level resistance, which had all mecA; 9 Staphylococcus aureus did not express beta-lactamase in low level resistance, among them, 5 Staphylococcus aureus had mecA. The difference in expression of beta-lactamase was statistically significant between MSSA and MRSA; MRSA(53.39%) was lower than MSSA (58.57%); the other differences were not significant. The difference in having mecA was statistically significant between MRSA(having high resistant level and no expression of beta-lactamase) and the others; MRSA had higher mecA than did the others. CONCLUSION: The resistance in Staphylococcus aureus mainly involved two mechanisms: the expression of beta-lactamase and the expression of mecA.