MRSA mecI基因和mec启动子的多态性研究

Evaluation of the genetic potymorphian of mecI and mec promoter region in MRSA

目的本研究的目的在于了解上海地区分离耐甲氧西林的金黄色葡萄球菌(MRSA)中mecI基因和mec启动子的多态性分布状况。方法收集上海地区分离的金黄色葡萄球菌143株,用头孢西丁纸片扩散试验、苯唑西林MIC(最小抑菌浓度)测定和mecA基因检测等方法进行MRSA的筛选,RAPD法进行细菌的同源性分析,最后通过PCR和序列分析技术研究分布状况。结果头孢西丁筛选试验、苯唑西林MIC试验与mecA基因PCR扩增相比有100％的一致性,均证实这些菌株为MR SA,RAPD法证实这些菌株分为4个型,在21株菌中有20株有mecI基因,所有的菌株有mec启动区,所有MRSA都有mecI或mec启动子的改变,其中mec的改变有mecI缺失、mecI 43位碱基G→T和mecI 202位碱基C→T。mec启动子的改变有G→T和C→A。结论mecI或mec启动子突变在临床分离的MRSA中普遍存在,上海地区MRSA以mecI 202位碱基突变最常见。

Objective To evaluate the genetic polymorphism of rnecl and mec promoter region in MRSA isolated from Shanghai region. Methods Cefoxitin disk diffusion test, determination of oxacillin MICs and detection of mecA gene were used to screen MRSA. And MRSA isolates were typed by randomly amplified polymorphic DNA （RAPD）. The sequences of mecl and the mec promoter region in 21 MRSA isolates were determined by PCR and sequence analysis method. Results The sensitivity and specificity of cefoxitin disk diffusion test for detection of MRSA had a 100% coherence rate with the result of mecA gene detection. The MRSA isolates were divided into 4 types （A to D） by RAPD, mecl was found in 20/21 strains and mec promoter region was found in all 21 MRSA isolates. All MRSA had mutations in mecl or mec promoter region. Mutations in mecl include deletion, G→T substitution at nucleotide position 43 and C→T at nucleotide position 202. And mutations in mec promoter region include G→T and C→A substitution. Conclusion Mutations in mecl gene and the mec promoter region are common phenomenon, and C→T mutation at nucleotide position 202 of mecl is the most common in clinical MRSA isolates.