Commercially available antiseptics show high efficacy against pathogens most commonly associated with canine and feline infectious keratitis.

PURPOSE

To determine the minimal bactericidal concentration (MBC) of polyhexanide (PHMB), povidone-iodine (PVP-I), N-acetylcysteine (NAC), and hypochlorous acid (HOCl) for bacterial species commonly found in canine and feline infectious keratitis.

METHODS

MBCs for clinical isolates of (.) ( = 11), including 3 methicillin-resistant strains, (.) ( = 8), and (.) ( = 11), including the corresponding control strains, were examined. All testing substances were serially diluted in phosphate-buffered saline (PBS) and cation-adjusted Mueller-Hinton Broth (CAMHB) and inoculated with the bacterial suspension for 10 min. Afterwards, a neutralisation with Dey-Engley neutralising broth was performed, followed by plating onto Columbia sheep-blood agar. After incubation, plates were visually examined for bacterial growth. Tests were carried out in triplicate.

RESULTS

MBCs in PBS for polyhexanide ranged 0.8-1.6 mg/L for and 1.6-3.2 mg/L for and . For povidone-iodine, MBCs in PBS were observed at concentrations ranging 8-32 mg/L for and and 8-16 mg/L for . MBCs in PBS for NAC were recorded at a range of 6,400-12,800 mg/L for , whereas those for and ranged 3,200-6,400 mg/L. Results for HOCl in PBS ranged 0.4-1.6 mg/L for and 0.4-0.8 mg/L for and . MBCs in CAMHB for polyhexanide were found in the range between 3.2 and >12.8 mg/L, those for povidone-iodine between 6,400 and >12,800 mg/L, and for NAC between 6,400 and >12,800 mg/L, across the tested species. When dissolved in CAMHB, no antimicrobial effect could be observed for HOCl in concentrations up to 137.5 mg/L.

CONCLUSION

All tested substances had an bactericidal effect against all three bacterial species with MBCs below known tolerated ocular concentrations when dissolved in PBS. Povidone-iodine and hypochlorous acid showed a marked reduction in their efficacy in the presence of protein. Nevertheless, our results provide a promising outlook on alternatives or adjuvants to antibiotics in ophthalmology that align with the One Health approach.