A lytic phage targeting virulent Proteus mirabilis for effective biofilm eradication.

Proteus mirabilis is an opportunistic pathogen frequently associated with catheter-associated urinary tract infections (CAUTIs), where robust crystalline biofilms contribute to chronicity, antimicrobial tolerance, and recurrence. The rising prevalence of multidrug-resistant (MDR) P. mirabilis has prompted interest in bacteriophage therapy as an alternative to conventional antibiotics. In this study, we isolated a lytic bacteriophage, vB_PmiM_ZX7, from sewage using a highly virulent clinical strain, P. mirabilis YV2, as the host. vB_PmiM_ZX7 displayed a broad host range among MDR P. mirabilis isolates and tolerance to a wide range of pH and temperatures. Genome sequencing revealed 60% of genes with unknown function, absence of virulence or antibiotic resistance genes, and limited similarity to known P. mirabilis phages, underscoring its genomic novelty. Safety evaluation in a murine model showed no adverse effect, histopathological changes, or persistent phage accumulation. Circulating phages were cleared from the blood within 5 h and from organs within 48 h. In anti-biofilm assays, vB_PmiM_ZX7 eradicated 62.2% of established biofilms, outperforming piperacillin/tazobactam (TZP), and significantly reduced extracellular polysaccharide content and biofilm density, as confirmed by scanning electron microscopy and fluorescence imaging. Furthermore, vB_PmiM_ZX7 demonstrated strong anti-biofilm activity in an in vitro catheter-associated biofilm model, markedly reducing the viability of biofilm-associated bacteria in a time-dependent manner. These findings demonstrated the potential of vB_PmiM_ZX7 as a therapeutic candidate for catheter-associated MDR P. mirabilis infections.