Comparison of the effectiveness of topical vancomycin and povidone-iodine treatments in methicillin resistant staphylococcus aureus keratitis model in rabbits

The aim of the study was to compare the efficacy of topical vancomycin and povidoneiodine (PI) on methicillin-resistant Staphylococcus aureus (MRSA) keratitis model in rabbits. For this purpose, after creating a keratitis model by applying 0.1 mL of MRSA strain containing 103 CFU to corneal centre of the right eyes of 24 rabbits, the rabbits were divided into 4 groups, with 6 rabbits in each group. 6 eyes in the first group were considered as the control group and received balanced salt solution (0.9% NaCl). Topical vancomycin was administered to the second group, topical PI to the third group, and topical vancomycin and PI to the fourth group. After the treatment, the corneas of the rabbits were removed using a vacuum trephine for microbiological analysis after euthanasia. We also evaluated and scored all corneas clinically regarding chemosis, conjunctival injection, iritis, fibrin, hypopyon, epithelial erosion, corneal infiltrate and corneal oedema parameters before and after treatment. The bacterial load was listed as follows; from highest to lowest, 7.63 ± 0.82 log10 CFU/g in the control group, 6.95 ± 1.66 log10 CFU/g in the PI group, 4.67 ± 0.77 log10 CFU/g in the topical vancomycin + PI group, and 4.33 ± 0.71 log10 CFU/g in the topical vancomycin group. When it comes to the comparison of the total clinical scores of MRSA keratitis before and after the treatment; 6.83 ± 1.16 vs. 12.16 ± 1.60 (p=0.001) in the control group, 6.16 ± 0.98 vs. 6.33 ± 1.03 (p=0.695) in the vancomycin group, 7.00 ± 1.09 vs. 12.00 ± 1.67 (p=<0.001) in the PI group, and 6.33 ± 0.81 vs. 8.16 ± 0.75 (p=0.002) in the vancomycin + PI group. When examining the post-treatment clinical scores in the groups; It was noteworthy that clinical scores deteriorated significantly in the control group, and the scores related to iritis, hypopyon and corneal infiltrate parameters were lower in the vancomycin-treated group. In the groups treated with PI, high scores were observed, especially in the parameters of chemosis, conjunctival injection and epithelial erosion. In conclusion, topical vancomycin was found to reduce bacterial load significantly in MRSA keratitis. However, PI was found not to be effective in reducing the bacterial load. On the contrary, PI was observed to have a toxic effect on the ocular surface. In addition, combining PI with vancomycin therapy was of no benefits on clinical and microbial outcomes.