Salicylate inhibition of Acanthamoeba attachment to contact lenses: a model to reduce risk of infection.

PURPOSE: Acanthamoeba attachment (adsorption) to hydrogel contact lenses is enhanced by Pseudomonas aeruginosa biofilm. The effect of sodium salicylate on Acanthamoeba attachment to biofilm-coated and uncoated hydrogel lenses was investigated.
DESIGN: Experimental study. PARTICIPANTS AND CONTROLS: A minimum of 16 replicates were used for each test condition; a control condition using clean lenses without biofilm was included.
METHODS: Four groups of hydrogel contact lenses (etafilcon A) were pretreated with P. aeruginosa to form a biofilm. In addition, two more groups remained untreated. Quartered lenses of all six groups were then incubated in a suspension of A. castellanii trophozoites. Two batches of lenses had either 3 or 30 mM sodium salicylate added to the bacterial suspension (stage 1 intervention). Two other batches of lenses had salicylate added to the amoebal suspension (stage 2 intervention). One of the batches, which had a stage 1 intervention, had salicylate added at the second stage as well. The remaining batches received no salicylate exposure and included lenses with and without biofilm coating. MAIN OUTCOME MEASURE: The outcome measure in this study was the number of Acanthamoeba trophozoites attached, per square centimeter, to the hydrogel surfaces.
RESULTS: Biofilm coating from P. aeruginosa gave a significantly increased attachment of A. castellanii trophozoites to the contact lens. When introduced at a first (biofilm) stage, second (trophozoite attachment) stage, or with intervention at both stages, 30 mM sodium salicylate reduced amoebal attachment to the hydrogel lens. When applied to both stages and when applied at stage 2 to the biofilm coated contact lenses, 3 mM sodium salicylate reduced amoebal attachment. The 3 mM concentration was not effective for the lower level of amoebae attachment to uncoated (nonbiofilm) lenses.
CONCLUSIONS: Sodium salicylate successfully reduced amoebal trophozoite attachment to hydrogel lenses. This was the result of one of the following possibilities or a combination thereof: inhibition of biofilm formation; a direct effect on the amoebae; an alteration in the biofilm-amoebal attachment and resulting modification of the hydrogel lens surface. The results of this study suggest the major action is at stage 2 (on amoebal attachment to lenses) and favors alteration of the biofilm-amoebal attachment mechanism. This study demonstrates salicylate's potential benefit as a component of contact lens care solutions, designed to reduce microbial attachment and the risk of infection.