Evaluation of active efflux in multidrug-resistant isolates of Acinetobacter baumannii

Abstract number: P2031

Abdi-ali A., Nikasa P., Falahi Z., Rahmani-badi A.

Objective: The purpose of this study was to evaluate of the contribution of active efflux in intrinsic multidrug resistance in clinical isolates of A. baumannii with emphasis on ciprofloxacin, gentamicin, ceftazidime and ethidium bromide (EtBr).

Methods: 65 clinical isolates were obtained throughout a one year period from different clinical samples (urine, blood, bone marrow and burns) from 3 hospitals. Isolates tested were all A. baumannii. Using Kirby-bauer drug susceptibility test for 12 antibiotics, 22 multidrug resistant strains which showed resistance to more than 10 of these antibiotics were screened for high resistance to ciprofloxacin, gentamicin, ceftazidime by determining MICs. Subsequently, to show that the high resistance in these strains depend on proton gradient-dependent efflux pump, MICs were also measured in presence and absence of carbonyle cyanide m-chlorophenyl hydrazone (CCCP), using microdilution method. CCCP was added to a concentration of 30 micro M.

Results: MIC for ciprofloxacin, gentamicin and ceftazidime were more than 64, 128 and 256 mg/ml, respectively. CCCP decreased the level of MICs at least in 1 dilution. Consequently the MICs in the presence of CCCP were lower than the MICs in the absence of the reagent.

Conclusion: This study indicates the MICs and accumulation of EtBr in the presence and absence of CCCP were different. These results demonstrate the presence of proton gradient-dependent efflux pumps in clinical isolates of A. baumannii.