Tailoring formulation for enhanced phage therapy in canine otitis externa: a cocktail approach targeting Pseudomonas aeruginosa and Staphylococcus pseudintermedius.

Canine otitis externa, characterized by the involvement of diverse bacterial species, notably Pseudomonas aeruginosa and Staphylococcus pseudintermedius, necessitates antibiotic administration as the primary therapeutic approach; however, prolonged treatment often precipitates antibiotic resistance. Therefore, the application of bacteriophages as antimicrobial agents has been of interest recently. However, phage therapy has limitations; its efficacy depends on the lytic capacity of the phage and the emergence of phage resistance, which can be overcome by using phage cocktails. This study aimed to enhance the therapeutic potential of bacteriophages by supplementing additional materials to hinder the pathogens and combining different viruses to broaden the lytic spectrum. The therapeutic potential of the phage cocktail, consisting of Pseudomonas phage pPa_SNUABM_DT01 and Staphylococcus phage pSp_SNUABM-J, was evaluated using an in vitro planktonic bacterial cell lysis assay and a biofilm degradation assay. Additionally, its efficacy was assessed using an in vivo mouse otitis externa model and clinical administration in five dogs with chronic Pseudomonas aeruginosa and Staphylococcus pseudintermedius otitis externa. The phage cocktail with formulation, including glycerol, glycine, and Tween 20, as additional components resulted in a significant reduction in bacterial counts and clinical improvements, including odor, discharge type and amount, and inflammatory symptoms. The results suggest that administering a phage cocktail solution with additional components could make phage therapy a more efficient treatment for otitis externa in dogs. This offers a practical alternative to traditional antibiotic treatments and could help mitigate antibiotic resistance in veterinary medicine.