To compare the antibacterial effects of vancomycin against 34 clinical methicillin resistant Staphylococcus (MRS) strains, in the combination with different β-lactams, rifampicin, gentamicin or erythromycin.The inhibitory zone of antibiotics was determined by disk diffusion method in the brain heart infusion agar (BHIA).Checkerboard synergy testing was performed by the agar dilution method in the BHIA. The fractional inhibitory concentration (FIC) index was calculated by adding the FICs (MIC of drug A in combination with drug B/MIC in drug A alone) of vancomycin and oxacillin, imipenem and rifampicin, repectively. Synergy between vancomycin and other antibiotics including penicillin, oxacillin, cefazolin, ceftazidime, imipenem, piperacillin/tazobactam, gentamicin, and erythromycin was also determined by a modified disk diffusion method. Disk diffusion test demonstrated that vancomycin could greatly enhance the antimicrobial activities of β-lactams against 6 strains of MRS. The diameter of the inhibitory zone of penicillin appeared to be the largest followed by those of oxacillin, cefazolin, imipenem, piperacillin/tazobactam and ceftazidime. Little or no enhancement effect by vancomycin was seen on erythromycin and gentamicin. The checkerboard showed that the synergistic rates of vancomycin combined with imipenem, oxacillin or rifampicin against 34 MRS strains were 91.2% (31/34), 85.3% (29/34), and 35.3% (12/34) respectively. The mean synergic rate of the three combinations against 9 strains of heterogeneously vancomycin-resistant staphylococci was100%, 100%, and 33.3% respectively. Results suggested although rifampicin in combination with vancomyicn was effective against MRS, it might not be considered as the first choice for such application because most of the tested β-lactams had showed better synergism with vancomycin in this study. The modified disk diffusion method could be used for screening available β-lactams to determine the best agents to pair with vancomycin for the control of MRS.%目的 比较万古霉素与不同β-内酰胺类、利福平、庆大霉素和红霉素分别联合对34株耐甲氧西林葡萄球菌的协同抗菌活性.方法 应用纸片扩散法测定不同抗生素纸片在脑心浸液琼脂板上的抑菌圈;棋盘协同试验应用琼脂稀释法;分数抑菌浓度指数由万古霉素与亚胺培南、苯唑西林和利福平联合获得的分数抑菌浓度的和.万古霉素与其它抗生素的协同作用包括青霉素、苯唑西林、头孢唑林、头孢他啶、亚胺培南、哌拉西林/三唑巴坦、庆大霉素和红霉素应用改良的纸片扩散法.结果 万古霉素明显增加β-内酰胺类抗菌药物对6株耐甲氧西林葡萄球菌的抗菌活性,青霉素的抑菌圈直径增加最大,其他依次为苯唑西林、头孢唑林、亚胺培南、哌拉西林/三唑巴坦和头孢他啶,对红霉素和庆大霉素的抑菌圈基本无影响.棋盘法显示万古霉素与亚胺培南、苯唑西林和利福平的联合协同百分比依次为91.2%(31/34)、85.3%(29/34)和35.3%(12/34),对9株万古霉素异质性耐药葡萄球菌的协同百分比依次为100%、100%和33.3%.结论 尽管万古霉素与利福平联合有协同作用,但不如万古霉素与β-内酰胺类抗菌药物联合的协同作用强.因此通过改良的纸片扩散协同试验选择与万古霉素最具协同作用的β-内酰胺类抗菌药物.
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