PSK1, a bacteriophage with antibacterial activity against extended-spectrum-beta-lactamase-producing Escherichia coli sequence type 131 with serotype O25:H4

The emergence of extended-spectrum-beta lactamase (ESBL)-producing E. coli sequence type 131 (ST-131) in urinary tract infections is a serious public-health threat. Here, we describe the isolation and characterization of a novel bacteriophage, PSK1, which exhibits antibacterial activity against multiple clinical strains of E. coli ST-131 with the O25:H4 serotype. This phage demonstrated strong lytic activity, achieving a 2-log reduction in infectivity at a multiplicity of infection (MOI) of 1, and complete growth inhibition at an MOI of 10 or 100. It was found to be stable for 24 hours in artificial urine and also exhibited stability at various pH values and temperatures, suggesting its potential use as a therapeutic agent for infections of the urinary tract and other tissues. PSK1 was found to have a latent period of 15 minutes and a burst size of 360 plaque-forming units (PFU) per infected cell. Transmission electron microscopy revealed a podovirus morphotype, with a capsid diameter of 104.97 ± 3.3 nm and a tail length of 33.56 ± 2.7 nm. The PSK1 genome is a double-stranded DNA molecule with a length of 39,615 base pairs, containing 61 open reading frames, encoding 25 proteins (41%) with a predicted function and 36 (59%) with no predicted function. PSK1 exhibits a purely lytic growth cycle and lacks any known virulence, antibiotic resistance, lysogeny, or mycotoxin genes. Lipopolysaccharide (LPS) inhibition assays showed that infection was blocked only by O25:H4-specific LPS, confirming the serotype specificity of this phage. A phylogenetic dendrogram based on proteomics analysis showed that PSK1 clustered with members of the family Autotranscriptaviridae, subfamily Studiervirinae, and genus Kayfunavirus, whose members employ a T7-like direct terminal repeat for genome packaging. Our data suggest that phage PSK1 is a strong candidate for bacteriophage therapy against uropathogenic E. coli ST-131 with the O25:H4 serotype.