Polyhexanide, Povidone‐Iodine, and Hypochlorous Acid Show High In Vitro Antimicrobial Efficacy Against Pathogens Commonly Associated With Equine Infectious Keratitis

OBJECTIVE: To determine the in vitro antimicrobial activity of specific antiseptics against common equine ocular surface pathogens. METHODS: Staphylococcus aureus (S. aureus) (n = 12), Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) (n = 9), Enterobacter hormaechei (E. hormaechei) (n = 6), and Bacillus cereus (B. cereus) (n = 5) were collected from corneal samples of horses with ulcerative keratitis. Reference strains were included. Minimum bactericidal concentrations (MBC) of polyhexanide, povidone-iodine, and hypochlorous acid were tested using the microdilution method. After incubation with the antimicrobial agent, the inocula were subcultured according to the Clinical and Laboratory Standards Institute guidelines. Colony growth was manually counted and photographically documented. RESULTS: The MBC values of polyhexanide were 0.8-3.2 ppm for S. aureus, 0.8-1.6 ppm for S. zooepidemicus, 1.6-3.2 ppm for E. hormaechei, and 1.6-6.4 ppm for B. cereus. For povidone-iodine, values were 8-32 ppm for S. aureus, 4-16 ppm for S. zooepidemicus, 8-16 ppm for E. hormaechei, and 8-16 ppm for B. cereus. For hypochlorous acid, values were 0.4-6.4 ppm for S. aureus, 0.4-3.2 ppm for S. zooepidemicus, 0.8-1.6 ppm for E. hormaechei, and 1.6-6.4 ppm for B. cereus. The MBC values of methicillin-resistant S. aureus isolates were comparable to those of methicillin-susceptible isolates. CONCLUSION: All antiseptics are highly efficient against common equine ocular bacterial surface pathogens, in concentrations that are well below those of commercially available products. In accordance with the One Health approach, these findings highlight their potential in treating infectious ocular surface disease either as an alternative or alongside topical antibiotics. Further in vivo and clinical studies are required to investigate the translatability of their in vitro effectiveness to clinic cases.