Combined drug sensitivity test of multiple drug resistant Pseudomonas aeruginosa in vitro

Objective To assess the in vitro inhibitory effect of meropenem（MEM） in combination with etimicin（ETM） or ciprofloxacin（CIP） on clinically isolated multiple drug resistant pseudomonas aeruginosa（MDRP） strains. Methods The minimum inhibitory concentration（MIC） of MEM in combination with ETM or CIP for 38 clinically isolated MDRP strains was measured with agar plate dilution method.The fractional inhibitory concentration（FIC）index of MEM in combination with ETM or CIP for the 38 MDRP strains was calculated. Results The synergic effect and additive effect of MEM in combination with ETM on MDRP strains was 63.2% and 36.8%,respectively,with no unrelated and antagonistic effect.The synergic effect,additive effect,and unrelated effect of in combination with CIP on MDRP strains was 73.5%,21.2% and 5.3%,respectively,with no antagonistic effect.The MIC50 and MIC90 of such drugs used in combination decreased significantly with their concentration-accumulative curves shifted to the left. Conclusion MEM in combination with ETM or CIP shows its in vitro inhibitory effect as synergic and additive effect on MDRP strains.