头孢噻呋单用及联合甲氧苄啶对致病性牛源大肠杆菌防突变浓度的研究

Study on the mutant prevention concentrations of ceftiofur alone and in combination with trimethoprim against pathogenic Escherichia coli from cattle

为了探讨体外头孢噻呋单用及与甲氧苄啶联用对致病性牛源大肠杆菌防突变浓度(MPC)的影响,试验选取对头孢噻呋敏感的8株致病性牛源大肠杆菌,采用微量肉汤稀释法和棋盘法测定头孢噻呋与甲氧苄啶单药及联合后的最小抑菌浓度(MIC),计算部分抑菌浓度指数(FIC指数),判断两药的相互作用;采用琼脂平板稀释法测定单药及联合后的MPC,并计算相应的选择指数(SI,SI=MPC/MIC)。结果表明:头孢噻呋与甲氧苄啶的FIC指数为0.25~1,两药联用呈协同或相加作用;头孢噻呋单用的MPC为64~512μg/m L,SI为64~256;与甲氧苄啶联合使用后MPC为16~32μg/m L,SI下降为8~64。说明头孢噻呋与甲氧苄啶联用可降低头孢噻呋单用对致病性牛源大肠杆菌的防突变浓度,缩小耐药突变选择窗。

To investigate the effects of ceftiofur alone and in combination with trimethoprim on the mutant prevention concentrations （ MPC ） against pathogenic Escherichia coli from cattle, 8 strains of pathogenic Escherichia coli from cattle that were sensitive to ceftiofur were selected in the test. The minimal inhibitory concentrations （MIC） of ceftiofur and trimethoprim alone and in combination with each other were determined by microdilution broth method and the checkerboard method, respectively. The fractional inhibitory concentration （ FIC ） indexes were calculated to judge the interaction between the two drugs. The MPC of both alone and in combination with each other were determined by the agar plate dilution method, and then the corresponding selective indexes （ SI, SI = MPC/MIC） were calculated, respectively. The results showed that the FIC indexes of ceftiofur and tfimethoprim were 0.25 to 1, and the combined use of the two drugs showed a synergistic or additive effect. The MPC of ceftiofur alone against 8 strains of pathogenic Escherichia coli were 64 to 512 μg/mL, and the corresponding SI were 64 to 256; the MPC of ceftiofur in combination with trimethoprim were 16 to 32μg/mL, and the corresponding SI decreased from 8 to 64. The results indicate that ceftiofur in combination with trimethoprim can lower the MPC of ceftiofur alone against pathogenic Escherichia coli from cattle and reduce the drug - resistant mutant selection window.