Isolation and characterization of a novel lytic bacteriophage vB_EcoS_P78 against multidrug-resistant Escherichia coli

Escherichia coli phage vB_EcoS_P78, a novel bacteriophage isolated from swine feces, exhibits typical siphovirus morphology with an isometric head and a non-contractile tail, forming clear plaques approximately 4 mm in diameter. It demonstrated a broad host range, lysing 75 % of tested ESBL-producing and MDR E. coli clinical isolates across multiple serogroups. The phage displayed strong stability, retaining activity at temperatures up to 50 °C and within a pH range of 3-10. Results from one-step growth assays showed a 20-minute latent period and that each infected cell produced a burst size of 220 PFU. Whole-genome sequencing revealed a 44,574 bp dsDNA genome containing 58 ORFs, with no antibiotic resistance, and virulence genes detected. Phylogenetic analysis based on intergenomic similarity and core protein phylogeny consistently supported its classification within the genus Dhillonvirus, showing 92.8 % similarity to Escherichia phage JL1. These results indicate that vB_EcoS_P78 represents a novel species of Dhillonvirus with potential therapeutic applications against multidrug-resistant E. coli.