Discovery of phage CSF, a novel generalist bacteriophage targeting multidrug-resistant and potentially pathogenic Staphylococcus spp. and Mammaliicoccus spp.

Antimicrobial resistance is escalating among Staphylococcus species, which are major pathogens affecting both humans and animals. As therapeutic options continue to narrow, phage therapy is re-emerging as a promising strategy to combat resistant strains. In this study, we isolated from pig farm effluents a bacteriophage named CSF, infecting a Staphylococcus xylosus strain. The CSF phage demonstrated a broad host range, lysing mecA-positive, multidrug-resistant strains across nine species of the genera Staphylococcus and Mammaliicoccus. Notably, it also inhibited biofilm formation in strains that it could not infect directly, and this activity persisted at low virus concentrations and in combination with antibiotics. The phage maintained its lytic activity under extreme conditions of temperature, pH, and UV exposure, underscoring its resilience for practical use. Sequencing of the viral genome revealed that it is 140 kb in length and has a genetic composition consistent with a lytic lifestyle. Phylogenetic analysis showed that phage CSF is related to members of the family Herelleviridae that are found globally, suggesting a widespread distribution of related viral lineages. Importantly, the phage genome was found to lack bacterial virulence or antimicrobial resistance genes, suggesting its safety for biotechnological applications. Intergenomic comparisons indicated that CSF should be classified as a member of a new genus, expanding the known diversity of bacteriophages. These findings demonstrate potential of CSF for phage therapy and other biotechnological applications.