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目的研究表皮葡萄球菌耐药机制,以指导感染性心内膜炎的治疗。方法取感染性心内膜炎患者血标本,培养分离表皮葡萄球菌,采用药敏试验,检测表皮葡萄球菌的耐药性;提取表皮葡萄球菌DNA,采用PCR扩增gyrA基因并测序,分析gyrA基因变异与喹诺酮类药物耐药的关系。结果药敏试验显示诺氟沙星、氧氟沙星、左氧氟沙星、培氟沙星、依诺沙星、环丙沙星对表皮葡萄球菌的MIC值分别为256、128、128、64、32、32μg/ml,耐药率分别为100.0%、80.0%、60.0%、60.0%、50.0%和30.0%;加替沙星对表皮葡萄球菌的MIC值为2μg/ml,即细菌对该药敏感。PCR扩增表皮葡萄球菌gyrA基因片段,大小为275bp。对gyrA基因测序,耐药株的107位发生了C到G的突变,36位氨基酸由Pro突变为Ala;耐药菌株的251位碱基发生由C到T的突变,相应编码的氨基酸由Ser突变为苯丙氨酸Phe;耐药株的336位C碱基缺失,发生错位突变;此外还发生了一些无义突变,如190位的T突变为G,223位的T突变为C。结论表皮葡萄球菌gyrA基因变异导致其对喹诺酮类抗菌药物产生耐药性,临床治疗表皮葡萄球菌所致的感染性心内膜炎时优先考虑使用加替沙星。
Objective To study the drug resistance mechanism of Staphylococcus epidermidis to guide the treatment of infective endocarditis. Methods Staphylococcus aureus was isolated from patients with infectious endocarditis, Staphylococcus epidermidis was cultured, drug resistance test was used to detect the drug resistance of Staphylococcus epidermidis, DNA of Staphylococcus epidermidis was extracted, and gyrA gene was amplified by PCR and sequenced. The gyrA gene Relationship between variation and quinolone resistance. Results The susceptibility test showed that the MIC values of norfloxacin, ofloxacin, levofloxacin, pefloxacin, enoxacin and ciprofloxacin were respectively 256, 128, 128, 64, 32μg / ml, the drug resistance rates were 100.0%, 80.0%, 60.0%, 60.0%, 50.0% and 30.0% respectively. The MIC value of gatifloxacin against Staphylococcus epidermidis was 2μg / ml. PCR amplification of Staphylococcus epidermidis gyrA gene fragment, the size of 275bp. The gyrA gene was sequenced. The mutation of C to G occurred at position 107 of the drug-resistant strain and the mutation of amino acid at position 36 from Pro to Ala. The mutation at position 251 of the resistant strain occurred from C to T, and the corresponding amino acid encoded by Ser Mutated to phenylalanine Phe; the C-terminal of the drug-resistant strain was deleted at position 336, and a mismatch mutation occurred. In addition, some nonsense mutations such as T at position 190 and G and T at position 223 were detected. Conclusion The mutation of gyrA gene of Staphylococcus epidermidis leads to its resistance to quinolone antibacterial drugs. Gatifloxacin is the first choice in the treatment of infective endocarditis caused by Staphylococcus epidermidis.