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

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.

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

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.

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.

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

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.