Biological Characteristics and Whole-Genome Analysis of Three Morphologically Distinct Staphylococcus aureus Phages

Staphylococcus aureus is an important zoonotic pathogen that threatens public health, food safety, and livestock production. Bacteriophages are promising antibacterial agents for controlling antimicrobial-resistant S. aureus, but their biological properties and genomic safety require systematic evaluation. In this study, three S. aureus phages, vB_SauL_202501, vB_SauM_202502, and vB_SauL_202503, were isolated from sewage samples and characterized by morphological observation, biological assays, whole-genome sequencing, and phylogenetic analysis. Transmission electron microscopy showed that vB_SauL_202501 and vB_SauL_202503 exhibited siphovirus-like morphology, whereas vB_SauM_202502 displayed myovirus-like morphology. Among the three phages, vB_SauM_202502 showed a relatively broader lytic spectrum and stronger sustained lytic activity in the spot assay. The optimal multiplicities of infection were 0.1, 0.1, and 0.01, respectively, and vB_SauL_202503 showed the shortest latent period, approximately 30 min. All three phages retained detectable infectivity at pH 5-10 and 4-37 °C, while vB_SauM_202502 maintained relatively high residual titers after heat treatment and ultraviolet irradiation. Genome analysis revealed double-stranded DNA genomes of 43,180-44,630 bp with GC contents of approximately 33.5%. No typical antimicrobial resistance genes or definitive auxiliary metabolic genes were identified. However, genes associated with lysogenic regulation, recombination, or immune modulation were detected in some phages, indicating that their lifestyles and application safety require further validation. These findings enrich S. aureus phage resources and provide a basis for the comparative characterization and safety assessment of candidate phages.