In vitro antimicrobial activity of a new ophthalmic solution containing hexamidine di-isethionate 0.05% (Keratosept®)

Purpose: To assess the in vitro antimicrobial activity of a new commercial ophthalmic solution containing hexamidine di-isethionate 0.05% (Keratosept®). Methods: Staphylococcus aureus ATCC 43300, Pseudomonas aeruginosa ATCC 27853, three ocular bacterial isolates (1 S. epidermidis, 1 S. aureus, 1 P. aeruginosa) and five Candida species were used. The bacterial and fungal isolates were cultured on Columbia blood agar base and Sabouraud-dextrose agar plates, respectively, and incubated overnight at 37°C. Suspensions in sterile saline solution were prepared to an optical density equal to 0.5 McFarland standard (~108 CFU/mL). Isolates suspensions were made in Keratosept® solution to obtain a concentration of 106 CFU/mL. The suspensions were then distributed in conical tubes in a final volume of 1 mL and incubated at 37°C. After 1, 5, 10, 15, 20, 25, 30 minutes and 24 hours, 10 μL of each suspension was removed, seeded on Columbia blood agar base and Sabouraud-dextrose agar plates and then incubated for 24 hours at 37ºC. Results: After 1-minute incubation, there was no growth on the plates seeded with S. aureus ATCC 43300, S. aureus clinical isolate, S. epidermidis clinical isolate, and all five Candida species tested. Conversely, Keratosept® solution failed to kill the Pseudomonas isolates after 30 minutes’ exposure and needed 24 hours to eradicate the organisms. Conclusion: Keratosept® ophthalmic solution showed in vitro antimicrobial activity against S. epidermidis, S. aureus, and Candida species. Results suggests that it may be a potential candidate for the treatment of staphylococcal and Candida infections of the ocular surface and have some role in antimicrobial prophylaxis before intravitreal injections.