Genomic and Biological Characterization of a Novel Proteus mirabilis Phage with Anti-Biofilm Activity

The emergence of multidrug-resistant (MDR) <i>Proteus mirabilis</i> poses a significant threat in porcine farming and public health, highlighting the need for alternative biocontrol agents. This study aimed to isolate and characterize a lytic bacteriophage with therapeutic potential against MDR <i>P. mirabilis</i>. Using the clinical MDR <i>P. mirabilis</i> strain Pm 07 as host, a bacteriophage, vB_Pmc_P-07 (P-07), was successfully isolated from fecal and sewage samples via an enrichment protocol. Phage P-07 forms plaques surrounded by a distinct translucent "halo," suggesting the production of depolymerase. It achieved high titers of up to 1.40 × 10⁸ PFU/mL and exhibited a narrow host range, high stability across a broad range of temperatures (40-60 °C) and pH (4-12), as well as considerable anti-biofilm activity. An optimal multiplicity of infection (MOI) of 0.001 was determined. Whole-genome sequencing revealed a linear double-stranded DNA genome of 58,582 bp with a GC content of 46.91%, encoding 63 open reading frames. Crucially, no virulence or antibiotic resistance genes were detected, supporting its safety profile. Phylogenetic analysis classified P-07 within the <i>Casjensviridae</i> family, closely related to phages PM87 and pPM01. These findings indicate that phage P-07 is a novel, safe, and effective lytic phage with strong potential as a biocontrol agent against biofilm-forming MDR <i>P. mirabilis</i> in swine.