In Vitro Antimicrobial Activity of N-Acetylcysteine against Pathogens Most Commonly Associated with Infectious Keratitis in Dogs and Cats

To determine the in vitro antimicrobial activity of N-acetylcysteine (NAC) against common pathogens associated with infectious keratitis in dogs and cats, clinical isolates of Staphylococcus (S.) pseudintermedius (n = 20), Streptococcus (St.) canis (n = 10) and Pseudomonas (P.) aeruginosa (n = 7) of canine and feline infectious ulcerative keratitis and a quality control strain (P. aeruginosa DSM 19880) were tested. The minimal inhibitory concentration (MIC) of NAC concentrations was determined using microdilution methodology. For S. pseudintermedius and P. aeruginosa, NAC concentrations in the range of 1.56 mg/mL (0.156%) to 100 mg/mL (10%), and for St. canis, concentrations ranging from 0.195 mg/mL (0.0195%) to 6.25 mg/mL (0.625%) were tested. For S. pseudintermedius, the MIC was 3.12 mg/mL (0.312%) for all tested isolates. For P. aeruginosa isolates and the quality control strain, the MIC ranged from 3.12 mg/mL (0.312%) to 6.25 mg/mL (0.625%). For St. canis, the MIC ranged from 1.56 mg/mL (0.156%) to 3.12 mg/mL (0.312%). NAC has an in vitro antimicrobial activity against three bacterial species commonly found in infectious keratitis in dogs and cats and therefore may be a promising alternative or adjuvant to topical antibiotics. The results warrant a clinical pilot study to assess the potential of NAC to reduce or replace the use of topical antibiotics in line with the One Health approach.