Adherence of Two Strains of Staphylococcus epidermidis to Contact Lenses

PURPOSE.To compare the adherence of biofilm-producer and nonbiofilm-producer Staphylococcus epidermidis in vitro to different soft contact lenses (CLs) to study its possible contribution to the pathogenesis of keratitis. METHODS.Strains of S. epidermidis slime-positive ATCC 35984 (biofilm-producer) and slime-negative ATCC 12228 (nonbiofilm-producer) were used with eight types of soft CLs from the four groups determined by the United States Food and Drug Administration (FDA), according to the ionicity and water content. The lenses were incubated overnight with the bacteria, then sonicated and vortexed to separate the adhered bacteria. Quantitative cultures were performed and the results statistically analyzed. RESULTS.Slime-negative strains of S. epidermidis were able to adhere to all CLs but at a lower level than slime-positive strains. There were significant differences in bacterial attachment among the four FDA groups. On the whole, there was higher bacterial adhesion to nonionic and low-water content materials. Contact lenses produced by soft molding were less adherent than CLs produced by either lathe-cutting or spin-casting. CONCLUSIONS.Bacterial biofilm favors bacterial adhesiveness and colonization of soft CLs. Bacterial attachment was less in soft molding CLs (etafilcon A), which provide a more homogeneous and smoother surface.