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Prevalence of efflux pump activity and its role in ciprofloxacin resistance in clinical isolates of Klebsiella pneumoniae

Abstract number: P1229

Aathithan S., French G.

Objectives: To determine the prevalence of efflux pump activity and its contribution to ciprofloxacin resistance in clinical isolates of Klebsiella pneumoniae.

Methods: Drug accumulation studies were performed on 26 ciprofloxacin susceptible and resistant isolates in early log-phase using [14C] ciprofloxacin with and without the proton motive force dissipater carbonyl cyanide 3-chlorophenylhydrazone (CCCP). The total accumulation time studied was 20 minutes; CCCP was added at 10 minutes. The efflux index, a measure of efflux activity, was the ratio of the amount of drug accumulated at the 18th minute to the amount accumulated at the 4th minute. Membrane-associated reduced influx-mediated resistance (MARIM-R) was calculated by dividing the difference in drug accumulation at the 10th and the 4th minutes (in the absence of CCCP) by the amount of drug accumulated at the 4th minute. Values of >1.5 were significant.

Results: (Table). 92% of tested isolates were positive for efflux. The contribution of efflux to the removal of cell-bound ciprofloxacin ranged from 50% to 90% of total cell-associated drug. In some highly resistant isolates efflux pump activity extruded 90% of the drug. Efflux activity was present in all isolates with ciprofloxacin MICs >1 mg/L and contributed to reduced ciprofloxacin susceptibility in isolates that had no target site alteration. High-level activity usually occurred in isolates with high ciprofloxacin MICs, but these isolates usually had double GyrA alterations as well. None of the 26 isolates had MARIM-R.

Conclusion: This study demonstrates that efflux activity is very common in K. pneumoniae and contributes to decreased ciprofloxacin susceptibility even in the absence of topoisomerase alterations. MARIM-R was not detected. Efflux activity may play a role in initial selection of isolates with reduced ciprofloxacin susceptibility, which then survive when ciprofloxacin is used. Surviving strains may then accumulate target site alterations and higher pump activity, leading to increasing ciprofloxacin resistance.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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