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Rodrigo A. Souza-Lima, Sr., Angelino J. Cariello, Marcelo Bispo, Sr., Gabriela De Souza, Sr., Marcelo De Oliveira, Ana Luisa Hofling-Lima, ACC Pignatari; Bactericidal Effect Of Nitric Oxide Donors Against Clinical Isolates From Keratitis. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5839.
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To evaluate the antimicrobial activity of two nitric oxide (NO) donors: S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylcysteine (SNAC) against clinical isolates from patients with infectious keratitis.
Reference microbroth dilution assays were performed to determine minimal inhibitory (MIC) and bactericidal (MBC) concentrations of GSNO and SNAC against 52 clinical isolates from patients with infectious keratitis. A hundred microliters of a bacterial suspension (5x105 cfu/ml) was added to 96-well microtiter plates containing 100 microliters of Mueller-Hinton Broth medium in pH 5 with 2-fold dilutions of GSNO and SNAC at a final concentration ranging from 0.31mM to 40mM. The plates were sealed and incubated at 37º and after 24h the MIC results were obtained (the lowest concentration without visible growth). One microliter from each well were cultured onto Tryptic Soy Agar and bacterial counting performed after an overnight incubation to determine the MBC. Mueller-Hinton Broth medium without bacteria and ATCC strains (S. aureus, S. epidermidis, P. aeruginosa and E. aerogenes) were also tested as negative and positive control, respectively.
The 52 clinical isolates included 13(25.0%) coagulase-negative Staphylococcus, 11(21.1%) Pseudomonas aeruginosa, 10(19.2%) Staphylococcus aureus, 9(17.3%) Serratia marcescens, 6(11.5%) Enterobacter aerogenes and 3 (5.8%) Pseudomonas pseudoalcaligenes. For Gram-positive bacteria, the MIC and MBC mean of SNAC were 2.1±1.3 and 8.6±3.8 mM, and, the MIC and MBC mean of GSNO were 4.6±3.2 and 21.4±12.5 mM, respectively(p<0.05). For Gram-negative bacteria, the MIC and MBC mean of SNAC were 3.3±1.4 and 6.1±3.4 mM and, the MIC and MBC mean of GSNO were 12.4±5.4 and 26.5±10.1 mM, respectively(p<0.05).
GSNO and SNAC showed bactericidal activity against clinical isolates from patients with infectious keratits. SNAC showed greater antimicrobial activity than GSNO against all bacteria. Gram positive bacteria showed to be more susceptive to bactericidal effect of NO-donors. These S-nitrosothiols showed to be potential ocular bactericidal drugs for the treatment of infectious keratitis.
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