title: Antimicrobial efficacy of chlorhexidine digluconate alone and in combination with eucalyptus oil, tea tree oil and thymol against planktonic and biofilm cultures of Staphylococcus epidermidis.
abstract: OBJECTIVE
  Effective skin antisepsis and disinfection of medical devices are key factors in preventing many healthcare-acquired infections associated with skin microorganisms, particularly Staphylococcus epidermidis. The aim of this study was to investigate the antimicrobial efficacy of chlorhexidine digluconate (CHG), a widely used antiseptic in clinical practice, alone and in combination with tea tree oil (TTO), eucalyptus oil (EO) and thymol against planktonic and biofilm cultures of S. epidermidis.
  
  
  METHODS
  Antimicrobial susceptibility assays against S. epidermidis in a suspension and in a biofilm mode of growth were performed with broth microdilution and ATP bioluminescence methods, respectively. Synergy of antimicrobial agents was evaluated with the chequerboard method.
  
  
  RESULTS
  CHG exhibited antimicrobial activity against S. epidermidis in both suspension and biofilm (MIC 2-8 mg/L). Of the essential oils thymol exhibited the greatest antimicrobial efficacy (0.5-4 g/L) against S. epidermidis in suspension and biofilm followed by TTO (2-16 g/L) and EO (4-64 g/L). MICs of CHG and EO were reduced against S. epidermidis biofilm when in combination (MIC of 8 reduced to 0.25-1 mg/L and MIC of 32-64 reduced to 4 g/L for CHG and EO, respectively). Furthermore, the combination of EO with CHG demonstrated synergistic activity against S. epidermidis biofilm with a fractional inhibitory concentration index of <0.5.
  
  
  CONCLUSIONS
  The results from this study suggest that there may be a role for essential oils, in particular EO, for improved skin antisepsis when combined with CHG.
authors.affiliation: School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK. karpantj@aston.ac.uk
authors.forename: T J
authors.initials: TJ
authors.lastname: Karpanen
authors.forename: T
authors.initials: T
authors.lastname: Worthington
authors.forename: E R
authors.initials: ER
authors.lastname: Hendry
authors.forename: B R
authors.initials: BR
authors.lastname: Conway
authors.forename: P A
authors.initials: PA
authors.lastname: Lambert
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects*; D002710:Chlorhexidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004357:Drug Synergism; D005052:Eucalyptus / Q000737:chemistry; D031650:Melaleuca / Q000737:chemistry; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D010938:Plant Oils / Q000494:pharmacology*; D013212:Staphylococcus epidermidis / Q000187:drug effects*; D013943:Thymol / Q000494:pharmacology*
chemical_list: D000890:Anti-Infective Agents; D010938:Plant Oils; D013943:Thymol; C010882:chlorhexidine gluconate; D002710:Chlorhexidine