Resistance of adhered bacteria to rigid gas permeable contact lens solutions

We examined eight conditioning or disinfecting solutions recommended for use with rigid gas permeable (RGP) or hard contact lenses for their efficacy against planktonic and attached cells of bacteria and Candida albicans. Most solutions, particularly those containing phenylmercuric nitrate and polyaminopropyl biguanide, gave marked inhibition (99.99% reduction within 4 hours) of planktonic cells of bacteria. Planktonic cells of Serratia marcescens and C. albicans survived in certain solutions containing chlorhexidine and benzalkonium chloride. In contrast, cells of all test microorganisms adhered to wells of polyethylene contact lens cases showed various degrees of survival after 4, 6, and 12 hours of exposure to most contact lens solutions. Drying of the lens case with adhered cells for 10 hours prior to addition of the lens solution usually reduced the incidence of recovery. Studies demonstrated that biofilms developed in cases with solutions of low and high efficacy. The enhanced resistance of adhered cells requires the periodic disinfection or replacement of lens cases used with RGP lenses.