Isolation, Characterization and In Vitro Evaluation of Novel Lytic Phages Active Against Staphylococcus aureus and Escherichia coli of Bovine Mastitis Origin

In this study, we report the isolation and characterization of novel lytic bacteriophages targeting Staphylococcus aureus and Escherichia coli, sourced from natural cases of bovine mastitis. Sewage and milk samples were collected from the livestock farm of the College of Veterinary and Animal Sciences (COVAS), Himachal Pradesh Agricultural University (HPAU), Palampur, Himachal Pradesh, India, as well as surrounding localities. The isolated phages were assessed for their lytic activity against S. aureus and E. coli across various temperatures and concentrations. Initial phage concentrations ranged from 10⁸ to 10⁹ PFU/mL. However, a reduction of 2–3 logs in phage concentration was observed after 9 months of storage, except for phages recovered from infected milk samples, which retained their lytic activity. Phylogenetic analysis revealed that the isolated phages belonged to the family Myoviridae. Furthermore, the lytic activity of these phages was found to be comparable to or even superior to that of conventional antibiotics tested. Moreover, the selected phages maintained their lytic activity in milk under in vitro conditions, underscoring their potential as therapeutic agents for the treatment of bovine mastitis.