Identification and Genomic Characterization of a Novel Teseptimavirus Species (vB_EcoP_S37A) and a Mosigvirus Phage (vB_EcoM_S37) Infecting Swine Extraintestinal Pathogenic Escherichia coli

The emergence of antimicrobial resistance in extraintestinal pathogenic Escherichia coli (ExPEC) necessitates alternative therapies for swine. Two lytic phages, vB_EcoM_S37 and vB_EcoP_S37A, were isolated from swine wastewater and characterized for morphology, stability, host range, antibacterial efficacy, and whole-genome features. Optimal multiplicities of infection were 0.01 and 0.1, respectively. Both phages remained stable at pH 4.0–11.0 and 40–60 °C. vB_EcoM_S37 lysed 43.55% (27/62) of tested E. coli strains, with a 5-min latent period and 1173 PFU/cell burst size, and suppressed bacterial growth for 12 h in vitro. vB_EcoP_S37A lysed 6.45% (4/62) of strains, exhibited a 10-min latent period and 210 PFU/cell burst size, and maintained inhibition for 8 h. Genomic analysis revealed that both phages have linear dsDNA genomes devoid of virulence or antibiotic resistance genes. vB_EcoM_S37 (173,927 bp, 37.42% GC) belongs to the genus Mosigvirus (family Straboviridae), whereas vB_EcoP_S37A (38,725 bp, 48.64% GC) represents a novel species within the genus Teseptimavirus (family Autotranscriptaviridae). These findings support both phages as stable, safe, and promising candidates for non-antibiotic biocontrol of ExPEC infections in livestock.