Antimicrobial efficacy of silver copolymerized barrel lens cases

Abstract

Purpose : Contact lens case contamination is common in daily contact lens wear despite the use of care systems. Silver impregnated contact lens cases were developed to reduce case contamination. In vitro studies evaluating the antimicrobial efficacy of silver-impregnated flat lens cases have demonstrated their robust activity against Gram negative bacteria including Pseudomonas aeruginosa. This study evaluated the in vitro antimicrobial activity of silver copolymerized barrel lens cases compared to control non-silver lens cases.

Methods : Silver copolymerized barrel lens cases and non-silver barrel lens cases (control) were evaluated against the test organisms Pseudomonas aeruginosa 6294, Serratia marcescens ATCC 13880, Acinetobacter sp. 22-1, Staphylococcus aureus 31 and Micrococcus sp. 22-1. Each bacterial strain was grown in tryptic soy broth at 37^oC for 24 hours. Contact lens cases were challenged with 10⁶ colony forming unit (CFU) bacterial suspensions. After 24 hrs incubation at 37^oC, bacteria were dislodged from the lens cases and serial dilutions plated onto nutrient agar. Surviving colonies were counted and the ability of the silver lens cases to reduce microbial colonisation was determined by comparing surviving organism on silver cases and control cases, using Mann-Whiney U test and Kruskal-Wallis test. Statistical significance was set at p <0.05.

Results : There were significantly lower numbers of recovered microbes from silver-copolymerized lens cases compared to control cases, for all the selected bacterial strains (p=0.02). Silver contact lens cases showed significantly higher activity against Gram positive bacteria compare to Gram negatives (p=0.04). The maximum inhibition in bacterial adhesion was 2.02±0.06 Log₁₀ CFU (p=0.008) against S. aureus 31. Compared with control cases, the silver cases reduced Micrococcus sp. 22-1 by 1.26±0.05 Log₁₀ CFU, followed by Acinetobacter sp. 22-1 by 1.51±0.03 Log₁₀ CFU, S. marcescens ATCC 13880 by 1.44±0.03 Log₁₀ CFU and P. aeruginosa 6294 by 1.26±0.07 Log₁₀ CFU.

Conclusions : Silver copolymerized barrel contact lens cases exhibited broad spectrum antimicrobial efficacy. Compared with non-silver barrel cases, silver barrel lens cases showed greatest activity against Gram positive bacteria.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.