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

Abstract

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.

N-Acetylcysteine and Its Immunomodulatory Properties in Humans and Domesticated Animals

“…Treatment of infectious keratitis involves topical antimicrobial treatment [136]. Due to the wide spectra of activity between antibiotics and the various bacterial strains involved, there is currently no antimicrobial agent available that is effective against all associated pathogens [136].…”

“…Due to the wide spectra of activity between antibiotics and the various bacterial strains involved, there is currently no antimicrobial agent available that is effective against all associated pathogens [136]. While some authors advise the use of a combination of different antimicrobial agents to treat this condition, this can potentially lead to reduced efficacy [136][137][138][139]. Many antibiotics are known to interfere with each other or even have antagonistic effects [139].…”

“…The bacterial microorganisms associated with infectious ulcerative keratitis in dogs, cats, and humans are also known to form biofilms [149][150][151][152]. While NAC is commonly used topically in human ophthalmology to treat corneal wounds, chemical injuries, keratitis, dry eye disease, and meibomian gland dysfunction, studies investigating the effect of NAC on pathogenic bacterial strains causing corneal ulceration in dogs and cats are lacking [136,153]. The study conducted by Walter et al (2023) appears to be the first study to be conducted to determine the in vitro antimicrobial activity of NAC against common pathogens associated with infectious keratitis in dogs and cats [136].…”

“…While NAC is commonly used topically in human ophthalmology to treat corneal wounds, chemical injuries, keratitis, dry eye disease, and meibomian gland dysfunction, studies investigating the effect of NAC on pathogenic bacterial strains causing corneal ulceration in dogs and cats are lacking [136,153]. The study conducted by Walter et al (2023) appears to be the first study to be conducted to determine the in vitro antimicrobial activity of NAC against common pathogens associated with infectious keratitis in dogs and cats [136]. NAC was observed to have an in vitro antimicrobial effect against all 38 bacterial isolates tested at relatively low concentrations (0.156-0.625%, 1.56-6.25 mg/mL) [136].…”

Effects of coenzyme Q10 and N-acetylcysteine on experimental poisoning by paracetamol in Wistar rats

“…For a long time, NAC has been used not only in cases of paracetamol intoxication, as an antioxidant, but also as an expectorant agent and in the treatment of keratitis and dry eye disease. New research refers to antimicrobial action against bacterial keratitis, interruption of biofilm formation and corneal healing [ 6 ], in addition to heart disorders caused by the use of doxorubicin [ 7 ]. However, although NAC is the drug of choice in PAR poisoning, coenzyme Q10 has successfully treated poisoning and disease [ 8 , 9 ].…”