To assess the in vitro antimicrobial activity of a new commercial ophthalmic solution containing hexamidine diisethionate 0.05% (Keratosept).
Staphylococcus aureus American Type Culture Collection (ATCC 43300), Pseudomonas aeruginosa ATCC 27853, 3 ocular bacterial isolates (1 Staphylococcus epidermidis, 1 S. aureus, and 1 P. aeruginosa), and 5 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 were prepared in a sterile saline solution with optical density equal to 0.5 McFarland standard (∼108 CFU/mL). Isolate suspensions were made in Keratosept solution to obtain a concentration of 106 CFU/mL. The suspensions were then distributed in conical tubes with 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 37°C.
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 5 Candida species tested. Conversely, Keratosept solution failed to kill the Pseudomonas isolates after 30 minutes exposure and needed 24 hours to eradicate the organisms.
Keratosept ophthalmic solution showed in vitro antimicrobial activity against S. epidermidis, S. aureus, and Candida species. Results suggest 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.