Influence of induced ciprofloxacin resistance on efflux pump activity of Klebsiella pneumoniae.

OBJECTIVE: The efflux pump (EP) is one of the major mechanisms of antibiotic resistance in Klebsiella pneumoniae. However, there are few reports on the effect of the abuse of antibiotic use on the activity of EPs. To determine whether the use of low efficacy antibiotics has any effect on the activity of EPs and induces drug resistance in K. pneumoniae, we investigated the effect of ciprofloxacin on the activity of EPs in K. pneumoniae strains. METHODS: Sixteen susceptible K. pneumoniae strains were isolated from patients and their minimum inhibitory concentrations (MICs) of ciprofloxacin were measured in the absence and presence of the pump inhibitor carbonyl cyanide m-chlorophenyl hydrazone (CCCP). The strains were then induced with a gradient of ciprofloxacin until the MICs of the strains showed no further increase, to obtain induced resistant strains. The EP activities of the strains before and after induction were compared using EP inhibition and ethidium bromide (EtBr) accumulation assays. RESULTS: The MIC values of the strains were 16‒256 times higher after induction than before induction. In the presence of CCCP, the MIC values of 50% of the induced strains were 2‒4-fold lower than that in the absence of this inhibitor. The EtBr accumulation assay showed that the fluorescence of EtBr in the induced cells was lower than that in the cells before induction. CONCLUSIONS: EPs are widespread in susceptible and drug-resistant K. pneumoniae strains. Induction with ciprofloxacin may increase the activity of EPs in K. pneumoniae. The EtBr accumulation assay is more sensitive than the EP inhibition assay in evaluating the activity of EPs in K. pneumoniae.