ABSTRACT
Objective To analyze the colistin heteroresistance in Pseudomonas aeruginosa strains and their in vitro susceptibility to antibiotics used in combination.Methods Two hundred and ninety-seven carbapenem-resistant Pseudomonas aeruginosa strains were selected for this study.Broth microdilution method was used to determine the minimum inhibitory concentrations of colistin and other antimicrobials against the Pseudomonas aeruginosa strains.The colistin heterogeneity of 20 colistin sensitive strains was analyzed by using population analysis profiles.The time-kill curves of 3 randomly selected colistin heteroresistant strains were used to determine the bacteriostatic activity of colistin.Chequer-board method was used to measure the combination efficacy of colistin with other antimicrobials including imipenem,meropenem,biapenem,ceftazidime,levofloxcin,piperacillin/tazobactam and cefoperazone/sulbactam.Results The colistin sensitive Pseudomonas aeruginosa strains accounted for 99.66％ of the 297 isolates.Population analysis profiles displayed that 35％ of the 20 isolates were colistin heteroresistant and 20％ of the 20 isolates were heterogeneous.It showed that when colistin was used in combination with other drugs,they mainly had synergistic and additive effects on heteroresistant isolates,but additive and indifferent effects on non-heterogeneous isolates.Conclusion Multidrug resistant Pseudomonas aeruginosa strains were highly susceptible to colistin,but heteroresistant and heterogeneous strains were common.The efficacy of colistin against heteroresistant isolates could be enhanced by using in combination with other drugs.