Antibacterial effect of N-acetylcysteine on common canine otitis externa isolates.

BACKGROUND: N-Acetylcysteine (NAC) has the potential to be a useful therapeutic agent for the treatment of otitis externa due to its antimicrobial and mucolytic properties, as well as its ability to disrupt bacterial biofilm.

HYPOTHESIS/OBJECTIVES: To determine the antibacterial activity of NAC against common bacterial isolates associated with canine otitis externa.

ANIMALS: Twenty two isolates from canine clinical cases of otitis externa were identified and tested, including five Staphylococcus pseudintermedius, six Pseudomonas aeruginosa, five Corynebacterium spp. and six β-haemolytic Streptococcus spp. isolates.

METHODS: Each isolate was grown on blood agar for 24 h and transferred to Mueller Hinton Broth (MHB) to achieve a final concentration of 5 × 10(5)  CFU/mL. NAC was diluted in MHB to a starting concentration of 160 mg/mL and serial two-fold microdilution assays were performed in triplicate with negative controls for all isolates tested. Concentrations of NAC tested ranged from 0.125 to 80 mg/mL. A 50 μL volume of bacterial suspension was used to inoculate each well.

RESULTS: The minimum inhibitory concentration (MIC) of NAC for all isolates tested ranged from 5 to 20 mg/mL.

CONCLUSIONS AND CLINICAL RELEVANCE: N-Acetylcysteine inhibits clinically relevant and drug resistant bacteria in vitro, and has potential for use as a novel agent for treatment of otitis externa.