Purpose: To investigate the ability of protamine, alone or in combination with other antimicrobial agents, to kill bacteria and fungi associated with contact lens–related keratitis.
Methods: The International Organization for Standardization 14729:2001 procedure was used to test the antimicrobial activity of solutions of protamine (23–228 μM) with and without polyhexamethylene biguanide (PHMB) and ethylenediamine tetra-acetic acid (EDTA). The recommended ISO panel of microbes along with six clinical isolates was tested. The effect of increasing sodium chloride concentration on the antimicrobial activity was also assessed. The cytotoxicity of the final protamine/EDTA/PHMB solution was measured using ISO 10993–5 standard assays.
Results: Protamine gave a dose-dependent antimicrobial effect, with the highest effect for most strains being at 228 μM (≥6 log reductions of viable bacteria and ≥1 log reduction of viable fungi). Addition of EDTA and PHMB increased the antimicrobial effect for all strains except Pseudomonas aeruginosa ATCC6538, which had optimum activity (≥6 log inhibition) even in protamine alone. The optimum antimicrobial activity of all microbes was achieved in 0.2% sodium chloride, but even in 0.8% sodium chloride, the activity met or exceeded the ISO standard (>3 log reductions for bacteria and >1 log reduction for fungi). None of the formulations was cytotoxic to mammalian cells.
Conclusions: This study highlights the potential for protamine to be used for the development of effective multipurpose disinfection solutions. Further investigations such as stability, compatibility with contact lenses, and in vivo toxicity are warranted.
Brien Holden Vision Institute (MKB, SM, HZ, RB), and School of Optometry and Vision Science (SM, HZ, RB, MDPW), University of New South Wales, Sydney, New South Wales, Australia.
Mark D. P. Willcox School of Optometry and Vision Science University of New South Wales Sydney, NSW 2052 Australia e-mail: firstname.lastname@example.org