Commercially available antiseptics show high in vitro effectivity against pathogens most commonly associated with canine and feline infectious keratitis

Hinrich Tönjes Wolff^1*Ana Cristina Piroth¹Hilke Oltmanns²Jessica Meißner²Jutta Verspohl³Holger Andreas Volk¹Claudia Busse^1*

• ¹Small Animal Clinic, University of Veterinary Medicine Hannover, Hanover, Germany
• ²Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hanover, Germany
• ³Institute for Microbiology, University of Veterinary Medicine Hannover, Hanover, Germany

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 Staphylococcus (S.) pseudintermedius (n = 11), including 3 methicillin-resistant strains, Pseudomonas (P. ) aeruginosa (n = 8) and Streptococcus (Str.) canis (n = 11), including the corresponding control strains, were examined.All testing substances were serially diluted in phosphate-buffered saline (PBS) and cationadjusted Mueller-Hinton-Broth (CAMHB) and inoculated with the bacterial suspension for 10 minutes. 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 from 0.8 -1.6 mg/l for S. pseudintermedius and from 1.6 -3.2 mg/l for P. aeruginosa and Str. canis. For povidone-iodine MBCs in PBS were observed at concentrations between 8 -32 mg/l for S. pseudintermedius and P. aeruginosa and between 8 -16 mg/l for Str. canis. MBCs in PBS for NAC were recorded at 6400 -12800 mg/l for S. pseudintermedius, whereas those for P. aeruginosa and Str. canis ranged from 3200 -6400 mg/l. Results for HOCl in PBS ranged from 0.4 -1.6 mg/l for S. pseudintermedius and from 0.4 -0.8 mg/l for P. aeruginosa and Str. canis.MBCs in CAMHB for polyhexanide were found in the range between 3.2 -> 12.8 mg/l, those for povidone-iodine between 6400 -> 12800 mg/l and for NAC from 6400 -> 12800 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.All tested substances had an in vitro bactericidal effect against all three bacterial species with MBCs below known tolerated ocular concentrations when dissolved in PBS. Especially povidone-iodine and hypochlorous acid showed a marked reduction in their in vitro efficacy in the presence of protein. Nevertheless, our results provide a promising outlook on alternatives or adjuvants to antibiotics in ophthalmology in line with the One Health approach.