Significance of Case Style in the Transfer of Pseudomonas aeruginosa to Contact Lenses During Storage Linda M. Ellis Department of Biology, York College of Pennsylvania ABSTRACT The leading cause of human keratitis in the United States is a Pseudomonas aeruginosa eye infection related to contact lens use. Though potentially blinding, keratitis is prevented by proper hygiene. This study’s objective was to compare the amount of bacteria transferred to lenses from infected cases of different styles. Three types of cases were inoculated with P. aeruginosa and incubated with a sterile contact lens. First, lens disinfection by commercial saline was evaluated as a negative control. Second, the level of bacterial transfer was assessed with varying incubation times and concentrations of salt solution. Finally, Ciba, Alcon and Bausch & Lomb brand cases were compared by incubating disposable contact lenses in nutrient broth and swirl-plating the broth in nutrient agar. Colonies were quantified by standard plate count and the results analyzed by nonparametric ANOVA (n = 10). The difference between the three case styles was not significant (p = ). METHODS P. aeruginosa grown In nutrient broth Ex. I Commercial Saline Ex. II Varied Time & Salt Solution with Serial Dilution Ex. III Varied Case Style Table 1. Percent salt concentrations and incubation times of cases in experiment II. % salt2824 0ABC 1DEF 5GHI 7JKL RESULTS Bacteria was not diluted or plated in experiment I because there was no growth from the lens placed in nutrient broth after 24-hours of incubation at 37° C. Figure one shows the growth on the plates from experiment II. There was a lawn on every 10 0 and 10 2 dilution plate. The most clearly differential colonies were obtained on plate L, which was incubated for 24-hours in a seven-percent salt solution and plated at a 10 6 dilution. The mean number of colonies grown from Ciba broth was 91.2, while the mean for Alcon was 72.5, and 43.7 for Bausch & Lomb. Each of the three categories of case style had a sample size of ten from five separate dilutions. The median number of colonies on the Ciba plates was 79, Alcon’s median was 75, and the median of colonies from Bausch & Lomb brand cases was 47. The Kruskal-Wallis nonparametric ANOVA test indicated that the variation among the medians was not significantly greater than expected by chance with a p value of Alcon™ commercial saline completely disinfects cases 2.Salt solutions are not an effective means of storage case disinfection 3.There is no significant difference between case styles in risk of bacterial transfer Add broth culture and lens to cases 1. Does commercial saline kill bacteria in storage cases? 2. What is the limit to disinfection? 3. Which case style is most prone to transfer bacteria to lenses? Acknowledgements: Barbara Taylor, lab instructor Ellis Eyes, optical supplies Dr. Jeffrey Thompson, PhD, senior thesis advisor INTRODUCTION There are more people in the world today who need visual correction than people with naturally perfect vision (Dart 1991). The most serious complication of contact lens wear is corneal inflammation, or keratitis. Bacterial keratitis, particularly when caused by the species Pseudomonas aeruginosa, can lead to blindness (Rosenfeld 1990). Manufacturers continuously test the disinfecting capacity of their saline solutions to prevent eye infections, such as keratitis. Yet, even sterile contacts can transmit bacteria to the eye when stored in an infected case. This study tests the ability of saline to prevent lens contamination from an unclean case. And, the probability of bacterial transfer from case to lens is compared between case styles. Incubate lenses in nutrient broth Swirl-plate and count colonies Incubation Time (hrs.) Questions Asked Conclusions Figure 1. Bacterial colonies growth from contacts stored in different brands of cases in experiment III. Literature Cited Dart, J.K., Stapelton, F. and Minassian, D Contact lenses and other risk factors in microbial keratitis. The Lancet 338: Rosenfeld, S.I. et al Granular epithelial keratopathy as an unusual manifestation of pseudomonas keratitis associated with extended-wear soft contact lenses. American Journal of Ophthalmology 109: DISCUSSION The total lack of growth in experiment I clearly exemplified the effectiveness of Alcon brand commercial saline. If lenses are properly disinfected there is virtually no risk of P. aeruginosa infection from contaminated storage cases as long as commercial saline is properly used. However, the risk of bacterial transfer increased proportionally with incubation time and inversely to salt solution concentration. Perhaps a greater sample size would indicate Bausch & Lomb as having the lowest risk of the three case style. While lens sit directly on the bottom of the flat cases, it suspends the lens above the infected case. Nonetheless, there is no significant difference in the risk of lens contamination from the three case types.