Esculentin-1a(1-21)NH sub(2): a frog skin-derived peptide for microbial keratitis

Pseudomonas aeruginosa is the primary bacterial pathogen causing contact lens related keratitis. Available ophthalmic agents have reduced efficacy and antimicrobial peptides (AMPs) hold promise as future antibiotics. Here we investigated the in vitro and in vivo anti-Pseudomonal activity of esculentin-1a(1-21)NH sub(2), derived from a frog skin AMP. The data revealed a minimum inhibitory concentration between 2 and 16 mu M against reference strains or drug-resistant clinical isolates of P. aeruginosa without showing toxicity to human corneal epithelial cells up to 50 mu M. At 1 mu M the peptide rapidly killed bacterial cells and this activity was fully retained in 150 mM sodium chloride and 70 % (v/v) human basal tears, particularly against the virulent ATCC 19660 strain. Furthermore, its dropwise administration at 40 mu M to the ocular surface in a murine model of P. aeruginosa keratitis (three times daily, for 5 days post-infection) resulted in a significant reduction of infection. The mean clinical score was 2.89 plus or minus 0.26 compared to 3.92 plus or minus 0.08 for the vehicle control. In addition, the corneal level of viable bacteria in the peptide treated animals was significantly lower with a difference of 4 log sub(10) colony counts, compared to 7.7 log sub(10) cells recovered in the control. In parallel, recruitment of inflammatory cells was reduced by half compared to that found in the untreated eyes. Similar results were obtained when esculentin-1a(1-21)NH sub(2) was applied prior to induction of keratitis. Overall, our findings highlight esculentin-1a(1-21)NH sub(2) as an attractive candidate for the development of novel topical pharmaceuticals against Pseudomonas keratitis.