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Patrick B Rapuano, Mariya Zyablitskaya, Shanta Modak, Leejee H Suh, Stephen Trokel, David C Paik; Sodium Hydroxymethylglycinate (SMG) for Therapeutic Tissue Crosslinking (TXL) of the Cornea: Antimicrobial Studies. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3525.
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Riboflavin/ultraviolet-A corneal collagen crosslinking is FDA approved and a well known treatment for keratoconus. Our recent studies raise the possibility of using SMG, a formaldehyde releaser (FAR), for pharmacologic TXL. The present study was performed in order to evaluate the known anti-microbial effects of FARs for SMG, a candidate compound for use as a TXL agent.
Methicillin sensitive Staphylococcus aureus (MSSA) and methicillin resistant Staphylococcus aureus (MRSA) were cultured in BBL™ Trypticase™ Soy Broth (TSB). From exponential growth phase, these bacteria were diluted to 3.3x103 colony forming units (CFU) per mL then 50uL of this culture was added to wells in a 96-well plate. Subsequently, 50uL of balanced salt solution (pH 7.5) with either 10mM, 20mM, or 40mM of SMG was added to each well and incubated for 10 minutes, 30 minutes, or 2 hours (N=5 per treatment). After incubation, the samples were diluted with 200uL of TSB and the entire diluted sample was spread on a BBL™ Trypticase™ Soy Agar plate and incubated for 24-48 hours at 37° Celsius. When colonies were grown sufficiently to be counted by the naked eye, colony counts were recorded.
Bactericidal activity of an SMG solution against MSSA in the 10-minute incubation group was modest for 10mM (30.6±5.0%), 20mM (39.1±5.3%), and 40mM (49.6±4.6%). These values increased in the 30-minute incubation group for 10mM (80.9±6.0%), 20mM (85.2±3.6%), and 40mM (91.7±0.9%%). The most robust bactericidal effect against MSSA was seen in the 2-hour incubation for 10mM (87.3±3.2%), 20 mM (94.1±0.8%), and 40mM (99.8±0.3%). In an additional round of experiments with 40mM SMG and a 2-hour incubation, the bactericidal effect was robust against MSSA (99.3±0.4%) and somewhat less robust against MRSA (95.9±1.5%).
SMG solution exhibits a dose-dependent bactericidal effect on MSSA. This solution is also an effective bactericidal agent against MRSA. Although prior studies have shown the efficacy of SMG against various strains of bacteria and fungus, this is the first report showing efficacy against MRSA, and increasingly troublesome bacteria with widespread effects. These studies underscore an exciting new possibility for the use of this agent in clinical therapeutics, including infectious keratitis, since these concentrations are well-tolerated in live rabbits.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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