Pantoea agglomerans in Equine Ulcerative Keratitis: Prevalence and Comparative Efficacy of Four Topical Antiseptics

ABSTRACT Objective To determine the minimal bactericidal concentration (MBC) and effective contact time of four topical antiseptics—polyhexanide, povidone‐iodine (PVP‐I), hypochlorous acid (HOCl), and N‐acetylcysteine (NAC)—against Pantoea agglomerans , a pathogen frequently isolated in equine ulcerative keratitis. Animals Studied Over a 17‐month sampling period, clinical isolates were collected from horses with ulcerative keratitis. The most frequently isolated strain ( Pantoea agglomerans , n = 14) was selected for in vitro analysis. Procedure(s) All isolates were used to determine the MBCs of the four antiseptics. Each was tested in triplicate at serial dilutions per isolate. Additionally, the requisite contact time for a bactericidal effect was evaluated at a supratherapeutic dilution for each substance with each isolate at defined time points ranging from 15 s to 5 min. Results The MBCs of polyhexanide, PVP‐I, HOCL, and NAC were 3.2 ppm (0.00032%), 16 ppm (0.0016%), 0.8 ppm (0.00008%), and 3200 ppm (0.32%), respectively. Polyhexanide (6.4 ppm), PVP‐I (64 ppm), and HOCL (6.4 ppm) were effective within 15 s. NAC (6400 ppm) required 1–2 min to achieve bactericidal effects. Conclusions All antiseptics tested demonstrated efficacy against P. agglomerans . Polyhexanide, PVP‐I, and HOCl achieved rapid bactericidal activity, while NAC required higher concentrations and longer exposure. These results support the use of these agents—particularly the faster‐acting three—as potential alternatives to antibiotics in treating equine ulcerative keratitis. They may aid the reduction of antibiotic use in line with the One Health approach.