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Does the presence of QAC genes in staphylococci affect the efficacy of disinfecting solutions used by orthokeratology lens wearers?
  1. Guang-sen Shi1,
  2. Maureen V Boost2,
  3. Pauline Cho1,2
  1. 1School of Optometry, The Hong Kong Polytechnic University, Hung Hum, Kowloon, Hong Kong
  2. 2Squina Centre for Infection Control, School of Nursing, The Hong Kong Polytechnic University, Hum Hom, Kowloon, Hong Kong
  1. Correspondence to Dr Maureen V Boost, School of Nursing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong; maureen.boost{at}polyu.edu.hk

Abstract

Background/aim There has been increasing evidence of the emergence of antiseptic resistance mediated by quaternary ammonium compound (QAC) resistance genes, which may reduce the efficacy of disinfection. Although the presence of QAC-positive staphylococci has been shown to be elevated in contact lens wearers, the efficacy of multipurpose solutions (MPS) against such isolates has not been determined. This study investigated the efficacy of four MPS for rigid gas permeable (RGP) lenses against staphylococci-harbouring QAC genes.

Methods Ability to reduce viability by three or more log reductions of four MPS for RGP lenses was tested against 60 disinfectant-resistant gene-positive staphylococci, comprising 38 coagulase-negative staphylococci (CNS) (17 qacA/B, 7 smr, 5 qacH, 9 habouring two or more genes) and 22 Staphylococcus aureus (16 qacA/B, 4 smr, 2 qacA/B+smr)). 60 gene-negative isolates of staphylococci (30 CNS and 30 S aureus) were used as controls. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of these four MPS were determined.

Results Although there was some variation between solutions, all failed to achieve a 3-log reduction in some S aureus and CNS isolates. Strains harbouring disinfectant-resistant genes were significantly less likely to be reduced by 3 logs by three of the solutions. Overall, the MIC and MBC of the four MPS against gene-positive clinical isolates were significantly higher than those of gene-negative isolates.

Conclusion The efficacy of MPS solutions for RGP lenses against staphylococci varied. The presence of disinfectant-resistance genes significantly adversely affected disinfecting capacity of RGP solutions.

  • Contact lens
  • Microbiology
  • Infection

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