title: Recently introduced qacA/B genes in Staphylococcus epidermidis do not increase chlorhexidine MIC/MBC.
abstract: OBJECTIVE
  Chlorhexidine is used as a disinfectant to prevent surgical infections. Recently, studies have indicated that chlorhexidine usage has selected methicillin-resistant Staphylococcus aureus strains that are tolerant to chlorhexidine and that this may be related to the presence of the qacA/B-encoded efflux pumps. Here, we evaluated if high-level exposure to chlorhexidine selects for tolerant colonizing Staphylococcus epidermidis and we addressed the consequences of long-term exposure to chlorhexidine.
  
  
  METHODS
  Chlorhexidine susceptibility and carriage of qacA/B was determined for colonizing S. epidermidis isolated from scrub nurses heavily exposed to chlorhexidine and were compared with isolates from non-users of chlorhexidine hand rubs. S. epidermidis blood isolates from the 1960s, before the wider introduction of chlorhexidine to the market, were also tested and compared with recently collected S. epidermidis blood isolates.
  
  
  RESULTS
  There was no correlation between the use of chlorhexidine in scrub nurses and the presence of qacA/B genes in S. epidermidis isolates or increased MICs/MBCs of chlorhexidine for S. epidermidis isolates. While 55% of current blood isolates harboured the qacA/B genes, none of the 33 historical S. epidermidis isolates did, although their MICs and MBCs of chlorhexidine were comparable to those for current isolates.
  
  
  CONCLUSIONS
  Chlorhexidine used as a hand rub does not select for S. epidermidis isolates with increased MICs or MBCs of chlorhexidine. However, the absence of qacA/B genes in S. epidermidis isolates obtained in the 1960s suggests that long-term use of biocides like chlorhexidine or related compounds may select for the presence of qacA/B genes.
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Sissel
authors.initials: S
authors.lastname: Skovgaard
authors.forename: Marianne Halberg
authors.initials: MH
authors.lastname: Larsen
authors.forename: Lene Nørby
authors.initials: LN
authors.lastname: Nielsen
authors.forename: Robert Leo
authors.initials: RL
authors.lastname: Skov
authors.forename: Christian
authors.initials: C
authors.lastname: Wong
authors.forename: Henrik
authors.initials: H
authors.lastname: Westh
authors.forename: Hanne
authors.initials: H
authors.lastname: Ingmer
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D002710:Chlorhexidine / Q000494:pharmacology*; D004202:Disinfectants / Q000494:pharmacology*; D004361:Drug Tolerance; D022761:Gene Transfer, Horizontal; D006235:Hand Disinfection / Q000379:methods; D006801:Humans; D017053:Infection Control / Q000379:methods; D026901:Membrane Transport Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009726:Nurses; D013212:Staphylococcus epidermidis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D001426:Bacterial Proteins; D004202:Disinfectants; D026901:Membrane Transport Proteins; C099272:QacB protein, Staphylococcus aureus; C068498:qacA protein, Staphylococcus aureus; D002710:Chlorhexidine
keywords: antimicrobial resistance; biocide susceptibility; hand rubs; hospital disinfection; infection control