Understanding and reducing microbial contamination of contact lens cases

Abstract

Microbes often contaminate contact lens storage cases during use. Up to 85% of contact lens storage cases show contamination by bacteria and contaminated lens cases may be associated with corneal infections and inflammation. This thesis sets out to understand how bacteria colonise cases, the kinetics and patterns of bacterial interactions during colonisation and determines how antimicrobial strategies might limit storage case contamination and deliver safer contact lens wear, both in laboratory studies and clinical trials. The rate of contact lens case contamination was estimated using a relatively new povidone iodine (cleadew™) based disinfecting system. Contact lens case contamination was low, with 30% of cases having no culturable microbes, but higher level of Gram-negative bacteria than some other disinfecting solutions. However, use of cleadew™ resulted in the recovery of multiple bacterial species from the same lens case. Subsequent experiments were designed to understand how multiple species may attach and colonise lens cases. My research demonstrated for the first time that ocular isolates of P. aeruginosa, S. aureus, A. radioresistens, M. luteus and Staphylococcus spp. could coaggregate. For P. aeruginosa and S. aureus coaggregation was not related to the build-up of biofilms in contact lens cases as there was no evidence that the coaggregation was associated with cohesion between the strains. However, A. radioresistens, M. luteus and Staphylococcus spp. coaggregated and cohered. Overall, these findings suggest that coaggregation and cohesion may occur and contribute to the coexistence of different microbial types in contact lens cases. Then I examined, whether antimicrobial silver-impregnated barrel cases could reduce the level of case contamination in vitro and in vivo. Silver was very effective in cases and resulted in significant decreases level of microbial colonization and lower levels of multispecies recovery from lens cases. This thesis revealed that the combined efficacy of silver in cases along with a disinfecting solution could be an approach to reduce overall bacterial contamination, particularly contamination by Gram positive bacteria. Further investigations are required to understand whether the microbes formed multispecies biofilms in lenses cases, and whether the reductions in lens case contamination result in reduced complications during lens wear.