The use of synthetic Cecropin (D5C) in disinfecting contact lens solutions

Abstract

Purpose: Microbial keratitis caused by Pseudomonas aeruginosa is the most common contact lens associated corneal infection. Cecropins are microbicidal peptides isolated from the hemolymph of the Cecropia moth. Previous in vitro studies have demonstrated their efficacy against a broad spectrum of ocular pathogens. This study was designed: a) to evaluate the antimicrobial potency of three different contact lens solutions (Renu, Complete, and Opti-Free) against P. aeruginosa, and b) to evaluate the activity of the same contact lens solutions in combination with a synthetic cecropin analog, D5C, against the challenge organism in the presence of a soft contact lens.

Methods: A virulent strain of P.aeruginosa isolated from a case of ulcerative keratitis was used in the study. Three different concentrations of bacteria (10(3), 10(5) and 10(7) CFU/mL) were inoculated into the contact lens solutions and into buffered saline, which was employed as a control. The samples were incubated at 27 degrees C, and at time 0, 30, and 90 minutes, 24, 48, and 72 hours, and aliquots of the test solutions were plated and subcultured on nutrient agar. After 24 hours of incubation at 37 degrees C, colonies observed on the nutrient agar plates were counted. To study the antimicrobial efficacy of D5C (100 micrograms/mL), we used the identical test series and assay, adding a soft contact lens to the solutions and a larger inoculum of bacteria (10(9) CFU/mL).

Results: After 72 hours, all of the contact lens solutions tested sterilized 10(3) CFU/mL of P. aeruginosa. At 10(7) CFU/mL, they yielded greater than 2 logs of killing of the bacteria, but the solutions were not sterilized. The addition of D5C (100 micrograms/mL) to the contact lens solutions yielded greater than 3 logs of killing with a larger inoculum of bacteria in the presence of the soft contact lens.

Conclusion: The contact lens solutions tested were effective against P. aeruginosa at 27 degrees C for up to 72 hours with an inoculum of 10(3) CFU/mL. The addition of D5C augmented their antimicrobial activity in the presence of the contact lens.