Efficacy of hydrogel contact lens disinfectants against Pseudomonas aeruginosa on soiled contact lenses.

Abstract

Abstract: : Purpose: We have shown that P. aeruginosa isolates vary considerably in their susceptibility to chemical contact lens disinfectants when basic inorganic ions are made available to the bacteria during testing. Resistance appears to be linked to acute cytotoxicity. The aim of this study was to investigate the effect of organically soiled contact lenses on disinfection susceptibility of cytotoxic and invasive P. aeruginosa strains. We hypothesized that disinfection would be less effective with organically soiled lenses compared to unsoiled lenses, and that cytotoxic P. aeruginosa strains would be more resistant to disinfection with soiled lenses than invasive strains. Methods: The disinfection susceptibility of 5 clinical and laboratory P. aeruginosa isolates (3 invasive, 2 cytotoxic) was investigated using laboratory–soiled contact lenses, unsoiled (new) lenses and disinfectant only controls. The FDA/ISO organic soil model was utilized and 4 disinfectants were assessed: A) preserved with polyquaternium–1 0.001% and myristamidopropyl dimethylamine 0.0005%, B), C) and D) preserved with polyhexamethylene biguanide (PHMB) 0.0001%. An initial inoculum of 5x10⁵ CFU/ml was achieved, and the number of bacterial survivors was determined at 4 and 6 h post–inoculation. Results: Susceptibility to solution A did not vary significantly between the P. aeruginosa strains when associated with soiled or unsoiled lenses. However, resistance to solutions B, C and D varied between strains, with poorer efficacy observed with soiled lenses compared to unsoiled lenses for at least one of the P. aeruginosa isolates (P<0.05). Solution A was the only disinfectant to achieve log reductions of at least 3.0 for all strains under all test conditions. Resistance to disinfection varied between cytotoxic and invasive strains for solutions B and D; invasive strains were more resistant than cytotoxic strains at 4 hours post–inoculation (P<0.05). Conclusions: P. aeruginosa isolates varied in their susceptibility to PHMB preserved solutions in the presence of soiled contact lenses, but did not vary in susceptibility to solution A. Invasive strains appeared to be more resistant than cytotoxic strains to two of the PHMB preserved solutions when associated with soiled lenses. Investigation of a wider range of cytotoxic and invasive isolates, and alternative soil models, will further enhance our understanding of P. aeruginosa resistance to contact lens disinfection.

Keywords: Pseudomonas • contact lens