title: Antimicrobial activity of chlorhexidine diacetate and benzalkonium chloride against Pseudomonas aeruginosa and its response to biocide residues.
abstract: OBJECTIVE
  The aims of this study were to evaluate the antimicrobial activity of chlorhexidine diacetate (CHX) and benzalkonium chloride (BZK) for strains of Pseudomonas aeruginosa exhibiting increased minimum inhibitory concentrations (MIC) for CHX, and to determine whether residues of chlorhexidine digluconate (CHG) and Hibiscrub (Hib, a formulation containing CHG) affect the susceptibility of P. aeruginosa to these biocides and a number of antibiotics.
  
  
  RESULTS
  The bactericidal activity of CHX and BZK was evaluated for strains of P. aeruginosa exhibiting increased MIC for CHX with established suspension and surface disinfection tests. None of the strains of P. aeruginosa exhibiting raised MIC for CHX was less sensitive than the parent strain to CHX or BZK in either method. A test was designed to investigate the effects of dried CHG and Hib residues on P. aeruginosa cells. Exposure of P. aeruginosa to dried residues of CHG or Hib did not result in the organism becoming less sensitive to either biocide or a number of antibiotics.
  
  
  CONCLUSIONS
  Pseudomonas aeruginosa strains with raised MIC to CHX were no less sensitive than the parent strain to CHX and BZK in bactericidal investigations. Exposure to dried residues of CHG and Hib did not render P. aeruginosa less sensitive to either of these agents or a number of antibiotics.
  
  
  CONCLUSIONS
  An increase in the MIC for a biocide in a micro-organism does not necessarily result in a failure of the biocide to effectively kill the organism. The residue that remains after the use of an antimicrobial agent can be at a far lower concentration than that initially applied and this study highlights the necessity for further investigations into the effect of residues, at low concentration, on bacterial populations and their role, if any, in the continued problem of antibiotic resistance.
authors.affiliation: Pharmaceutical Microbiology Research, Welsh School of Pharmacy, Cardiff University, Cardiff, UK.
authors.forename: L
authors.initials: L
authors.lastname: Thomas
authors.forename: A D
authors.initials: AD
authors.lastname: Russell
authors.forename: J-Y
authors.initials: JY
authors.lastname: Maillard
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001548:Benzalkonium Compounds / Q000494:pharmacology*; D002710:Chlorhexidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004202:Disinfectants / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial; D004783:Environmental Microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D001548:Benzalkonium Compounds; D004202:Disinfectants; C010882:chlorhexidine gluconate; D002710:Chlorhexidine