effect of efflux pump inhibitor carbonyl cyanide 3-chlorophenylhydrazone on the minimum inhibitory concentration of ciprofloxacin in acinetobacter baumannii clinical isolates

background: acinetobacter baumannii is an important human pathogen with increasing notoriety in the recent years, as a causative organism of drug resistant nosocomial infections, particularly in immunocompromised patients hospitalized in burn centers. objectives: the aim of this study was to determinate the role of efflux pump(s) in ciprofloxacin resistance of a. baumannii strains isolated from burn patients. materials and methods: sixty-five a. baumannii strains were isolated from the burn patients hospitalized in motahari burns and reconstruction center in tehran, iran. susceptibility test to ciprofloxacin was carried out by disk agar diffusion and agar dilution methods, according to the clsi guidelines. activity of the efflux system was evaluated using efflux pump inhibitor carbonyl cyanide 3-chlorophenylhydrazone (cccp). results: all acinetobacter isolates were resistant to ciprofloxacin. the minimum inhibitory concentration (mic) range of ciprofloxacin in isolates was 4 to 128 µg/ml or greater. moreover, susceptibility of strains to ciprofloxacin was highly increased in the presence of efflux pump inhibitor; so that, for 86.1% (56/65) of isolates, cccp reduced the mic by 2 to 64 folds. conclusions: our findings are suggestive that efflux-based system may play a role in fluoroquinolone resistance in a. baumannii isolates, affecting hospitalized patients. the ability of acinetobacter to acquire resistance to these potent antimicrobials by the efflux pump mechanism is a concern. therefore, new strategies are required in order to eliminate the efflux transport activity from the resistant bacteria causing nosocomial infections and provide more appropriate approaches for treatment and management of troubling infections.