Systematic characterization of four novel Twort-group bacteriophages infecting Staphylococcus hyicus

Exudative epidermitis (EE) in piglets, caused by the bacterium Staphylococcus hyicus, remains a major concern for the swine industry, particularly due to antimicrobial resistance. Bacteriophages represent a promising alternative treatment. This study aimed to isolate and characterize phages infecting S. hyicus from EE-affected swine farm environments in Quebec. Four novel phages (BQE1, BQE4, BQE7, BQL4) were isolated from water and manure samples. All produced clear plaques (<1 mm) and reached titers of 10⁸-10¹⁰ PFU/mL. Electron microscopy revealed myovirus morphology. Their genomes (115.4-134.5 kb) are closely related to the already described Twort phage but distinct from other S. hyicus phages. No virulence or antimicrobial resistance genes were detected in their genome. Host range analysis across 58 staphylococcal strains showed broad activity against S. hyicus (77%-80% susceptibility), whereas the Twort phage was largely ineffective (4%). Adsorption and growth assays indicated efficient infection, with latent periods of ∼50 min and burst sizes of 10-13 PFU/cell. Phages remained stable at 4 °C and room temperature but were less stable at 31 °C. Overall, these Twort-like phages display strong lytic activity and favorable genomic and biological characteristics, supporting their potential as targeted alternatives to antibiotics for controlling EE in swine production.