The in vitro efficacy of eye drops containing a bacteriophage solution specific for Staphylococcus spp. isolated from dogs with bacterial conjunctivitis

Abstract

Background: The purpose of the study was to evaluate the in vitro antibacterial effect of experimental eye drops with bacteriophages in elimination of Staphylococcus spp. isolated from dogs with bacterial conjunctivitis. The bacterial material was collected from dogs with independent clinical signs of bacterial conjunctivitis. Staphylococcus spp. were identified by phenotypic and genotypic methods (MALDI-TOF MS mass spectrometry). Antibiotic resistance was determined by the disc-diffusion method. Phage activity (Plaque forming units, PFU) was determined on double-layer agar plates. Phages with lytic titres > 108 PFU were used to prepare eye drops. The stability of the antibacterial titre was evaluated for preparations stored in sealed bottles as well as after opening and reclosing. Results: The tests confirmed the occurrence of Staphylococcus spp. strains as etiological agents of bacterial conjunctivitis in dogs. A high percentage of strains were resistant to more than three antibiotics. The experimental phage eye drops used in the study exhibited 100% efficacy in vitro against the tested Staphylococcus isolates. Particularly noteworthy is the long duration of activity and constant antibacterial lytic titre of ≥108 PFU/mL of two eye drop solutions, nos. 7 and 12, after the bottle had been opened (21 days) and after hermetically sealed packaging (28 days) at 4–8 °C. Conclusions: The results represent the first stage of research and require continuation in vivo. If positive effects are obtained in animals, the results can be used in applied research in humans and animals.