Pantoea agglomerans in equine ulcerative keratitis : prevalence and comparative efficacy of four topical antiseptics

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.