The in vitro antibacterial activity of the anthelmintic drug oxyclozanide against common small animal bacterial pathogens

Background: Repurposing existing drugs is one approach to address the growing concerns of multi-drug resistant Bacterial pathogens in veterinary medicine. Oxyclozanide is in the anthelmintic drug class salicylanilide, which has been used primarily as a treatment and preventative for Fasciola hepatica in ruminants. The antimicrobial activity of oxyclozanide has been studied in human medicine; its activity against common small animal Bacterial pathogens such as Staphylococcus pseudintermedius has yet to be determined.

Objective: The aim of this study was to measure and establish the minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) of oxyclozanide against S. pseudintermedius and other common small animal Bacterial pathogens.

Methods and materials: The MIC and MPC of oxyclozanide were determined from eighteen meticillin sensitive S. pseudintermedius (MSSP) isolates and eleven meticillin-resistant S. pseudintermedius (MRSP), as well as single isolates of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis.

Results: The MIC of the eighteen meticillin-sensitive S. pseudintermedius isolates was 0.5-1 μg/mL and the MPC ranged between 16 and 32 μg/mL. The MIC of the eleven meticillin-resistant strains of S. pseudintermedius ranged from 0.5 to 2 μg/mL with a MPC ranging between 16 and 32 μg/mL. A single isolate of meticillin-resistant S. aureus (MRSA) had an MIC of 1 μg/mL and MPC 16 μg/mL. No inhibition of growth was seen at the concentrations tested for Bacterial isolate strains E. coli, P. aeruginosa and E. faecalis.

Conclusion and clinical importance: Oxyclozanide demonstrated in-vitro Antibacterial activity against meticillin-resistant S. pseudintermedius. Further studies are needed to evaluate the potential use of oxyclozanide as a topical bactericidal agent.