title: Prevalence and role of efflux pump activity in ciprofloxacin resistance in clinical isolates of Klebsiella pneumoniae.
abstract: We investigated the prevalence and role of efflux pump activity and possible drug influx resistance in ciprofloxacin susceptibility amongst 26 distinct clinical isolates of Klebsiella pneumoniae of varying ciprofloxacin susceptibilities and known quinolone resistance-determining region (QRDR) genotypes. Cellular [(14)C]ciprofloxacin accumulation patterns and the amount of cell-associated [(14)C]ciprofloxacin of mid-logarithmic phase cells were determined before and after challenging with the efflux pump inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Most isolates (24/26), and all with ciprofloxacin minimum inhibitory concentrations (MICs) >1 µg/ml, had efflux activity that could extrude up to 90% of cell-associated [(14)C]ciprofloxacin; none had significant influx resistance. In isolates with no QRDR mutations, efflux alone reduced ciprofloxacin susceptibility. In isolates with QRDR mutations, the efflux activity varied: in one isolate with no efflux activity, the most common fluoroquinolone resistance-causing QRDR mutation did not bring about clinically significant ciprofloxacin resistance; isolates with multiple mutations had high MICs and, usually, high levels of efflux activity. Fluoroquinolone efflux activity is much more common in clinical isolates of K. pneumoniae than previously reported and it can contribute to decreased ciprofloxacin susceptibility.
authors.affiliation: King's College London, Department of Infectious Diseases, Division of Immunology, Infection and Inflammatory Diseases, School of Medicine, London SE1 7EH, UK. sivasampu.aathithan@kcl.ac.uk
authors.forename: S
authors.initials: S
authors.lastname: Aathithan
authors.forename: G L
authors.initials: GL
authors.lastname: French
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001693:Biological Transport, Active; D002250:Carbon Radioisotopes / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000378:metabolism; D002939:Ciprofloxacin / Q000378:metabolism / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D005798:Genes, Bacterial; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology*; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D013194:Staining and Labeling / Q000379:methods; D014475:Uncoupling Agents / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D002250:Carbon Radioisotopes; D026901:Membrane Transport Proteins; D014475:Uncoupling Agents; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D002939:Ciprofloxacin