title: Reduced susceptibility to chlorhexidine among extremely-drug-resistant strains of Klebsiella pneumoniae.
abstract: BACKGROUND
  Over the last decade, extremely-drug-resistant (XDR) strains of Klebsiella pneumoniae have emerged worldwide, mainly as a result of patient-to-patient spread. The predominant clone, sequence type 258 (ST258), is associated with high morbidity and mortality, and is a worldwide threat to public health. It was hypothesized that reduced susceptibility to chlorhexidine, the most widely used hospital disinfectant, may contribute to the endemic nature of this strain.
  
  
  OBJECTIVE
  To characterize and compare the susceptibility of the epidemic K. pneumoniae clone ST258 and non-epidemic K. pneumoniae clones to chlorhexidine.
  
  
  METHODS
  The minimum inhibitory concentration (MIC) of chlorhexidine was determined in 126 XDR K. pneumoniae clinical isolates using agar dilution. Expression of three different efflux pumps -cepA, acrA and kdeA - was investigated in the absence and presence of chlorhexidine using quantitative real-time polymerase chain reaction. Heteroresistance to chlorhexidine was identified using population analysis.
  
  
  RESULTS
  The MIC of chlorhexidine was higher for K. pneumoniae ST258 (N = 70) than other K. pneumoniae sequence types (N = 56); 99% of ST258 isolates had MICs >32 μg/mL, compared with 52% of other K. pneumoniae sequence types (P < 0.0001). Reduced susceptibility to chlorhexidine appeared to be independent of the expression of cepA, acrA and kdeA efflux pumps. Chlorhexidine-resistant subpopulations were observed independent of the bacterial sequence type or the MIC.
  
  
  CONCLUSIONS
  Reduced susceptibility to chlorhexidine may contribute to the success of XDR K. pneumoniae as a nosocomial pathogen, and may provide a selective advantage to the international epidemic strain K. pneumoniae ST258. The heterogeneous nature of chlorhexidine-resistant subpopulations suggests that this phenomenon might not be rendered genetically.
authors.affiliation: Molecular Epidemiology and Antimicrobial Resistance Laboratory, Division of Epidemiology, Tel Aviv Medical Centre, affiliated to the Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: L
authors.initials: L
authors.lastname: Naparstek
authors.forename: Y
authors.initials: Y
authors.lastname: Carmeli
authors.forename: I
authors.initials: I
authors.lastname: Chmelnitsky
authors.forename: E
authors.initials: E
authors.lastname: Banin
authors.forename: S
authors.initials: S
authors.lastname: Navon-Venezia
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D002710:Chlorhexidine / Q000494:pharmacology*; D003428:Cross Infection / Q000382:microbiology; D004202:Disinfectants / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D020869:Gene Expression Profiling; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests / Q000379:methods; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D001426:Bacterial Proteins; D004202:Disinfectants; D002710:Chlorhexidine