DOES ACANTHAMOEBA PROTECT PSEUDOMONAS-AERUGINOSA FROM THE BACTERICIDAL EFFECTS OF CONTACT-LENS DISINFECTING SYSTEMS

Purpose: The aim of this study was to test the hypothesis that Pseudom onas aeruginosa that have been internalized in Acanthamoeba are protec ted against the action of contact lens disinfecting solutions. Methods : The experiments were divided into two parts. First, five commerciall y available disinfecting solutions, hydrogen peroxide and non-peroxide based, were tested for their efficacy against four strains of P. aeru ginosa and one strain of A. castellanii. Cells were inoculated in-to w orking concentrations of disinfecting solutions, incubated for 18 h an d the numbers of viable bacteria or amoeba were analysed after appropr iate growth on agar plates. Second, two strains of P. aeruginosa were allowed to interact with A, castellanii for 4 h prior to addition to d isinfecting solutions. The numbers of P. aeruginosa after incubation w ith the disinfecting solutions were measured after growth on agar plat es. Results: In general, disinfecting solutions containing hydrogen pe roxide were most effective against the micro-organisms. Solutions cont aining only traces of polyaminopropyl biguanide were least effective. Conclusions: For strains of P. aeruginosa, the presence of the amoebae did not protect the bacteria against the disinfecting agents.The amoe ba appeared to kill the bacteria, perhaps using them as a food source.