Antimicrobial resistance is increasing in both human and veterinary medicine. Bacteria can be part of the etiology of respiratory disorders in horses. Bactericidal activity of silver has been largely described and silver is currently used in veterinary therapeutic applications such as wound dressings. The aim of this study was to assess the in vitro bactericidal effects of nebulized silver nanoparticles (AgNP) on 2 common equine respiratory bacteria, Streptococcus equi subsp. zooepidemicus and Actinobacillus equuli subsp. equuli. Firstly, antimicrobial susceptibility of AgNP was determined over time by turbidity assessment in liquid broth. Secondly, bacterial growth inhibition was tested after instillation or after nebulization of low (100 ppm) and high (500, 1,000 and 2,000 ppm) concentrations of AgNP on agar plate. Both bacteria were susceptible to AgNP, even at dilution 1:4 for A. equuli and 1:8 for S. zooepidemicus after 8 hours of incubation, and 1:256 for both bacteria after 24 hours of incubation. The bacterial growth was partially inhibited at low concentration and completely inhibited at high concentrations of instilled AgNP. The bacterial growth was completely inhibited after nebulization of low concentrations of AgNP for A. equuli and high concentrations of AgNP for S. zooepidemicus. We concluded nebulized AgNP could be a candidate for innovative therapeutic way against bacterial respiratory disorders in horses. Nevertheless, further investigations are required to assess the in vivo potential and toxicity of nebulized AgNP.
Keywords: Aerosol therapy; Airway; Bacteria; Silver.
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