Does Acanthamoeba protect Pseudomonas aeruginosa from the bactericidal effects of contact lens disinfecting systems?
OBJECTIVE
The aim of this study was to test the hypothesis that Pseudomonas aeruginosa that have been internalized in Acanthamoeba are protected against the action of contact lens disinfecting solutions.


METHODS
The experiments were divided into two parts. First, five commercially available disinfecting solutions, hydrogen peroxide and non-peroxide based, were tested for their efficacy against four strains of P. aeruginosa and one strain of A. castellanii. Cells were inoculated into working concentrations of disinfecting solutions, incubated for 18 h and the numbers of viable bacteria or amoeba were analysed after appropriate growth on agar plates. Second, two strains of P. aeruginosa were allowed to interact with A. castellanii for 4 h prior to addition to disinfecting solutions. The numbers of P. aeruginosa after incubation with the disinfecting solutions were measured after growth on agar plates.


RESULTS
In general, disinfecting solutions containing hydrogen peroxide were most effective against the micro-organisms. Solutions containing 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 amoeba appeared to kill the bacteria, perhaps using them as a food source.
School of Optometry, and Cooperative Research Centre for Eye Research and Technology, University of New South Wales, Sydney, Australia. M.WILLCOX@CCLRU.RANDWICK.UNSW.EDU.AU
M D
MD
Willcox
R
R
Low
J
J
Hon
N
N
Harmis
D000048:Acanthamoeba / Q000187:drug effects / Q000382:microbiology* / Q000502:physiology; D000818:Animals; D001645:Biguanides / Q000494:pharmacology*; D015169:Colony Count, Microbial; D018639:Contact Lens Solutions / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000502:physiology*
D001645:Biguanides; D018639:Contact Lens Solutions; C064420:polyaminopropylbiguanide; D006861:Hydrogen Peroxide