Biological characterization of multidrug-resistant <i>Pseudomonas aeruginosa</i> phage PaeP_Ls and its efficacy in septic mice

With the widespread use of antibiotics, multidrug-resistant <i>Pseudomonas aeruginosa</i> (MRPA) is increasing year by year. Phage therapy is gaining more and more attention as an alternative therapy to antibiotics. The main objective of this study was to assess the efficacy of PaeP_Ls phage against MRPA-induced sepsis in mice. We isolated and purified a lytic <i>P. aeruginosa</i> phage PaeP_Ls. PaeP_Ls had an optimal multiplicity of infection (MOI) of 0.001 under our conditions, latent and lytic periods of 25 and 70 min, and a burst size of about 50 plaque-forming units (PFU) per infected cell. Its lysis rate against MRPA was 53.33%. PaeP_Ls was a double-stranded DNA virus with a genome length of 45,217 bp and GC content of 52.46%, encoding 81 coding sequences and three tRNAs, without drug resistance genes or virulence factors. We used PaeP_Ls to treat the <i>P. aeruginosa</i> strain MRPA1-infected septic mice and found that intraperitoneal injection of high concentrations of PaeP_Ls (MOI = 10) significantly increased the survival rate of the mice (<i>P</i> < 0.0001). Intraperitoneal injection of (5 × 10¹¹ PFU/mouse) phage in septic mice caused a significant reduction in the bacterial load in the blood of the mice. Histopathology showed that inflammatory cell infiltration and congestive edema were significantly reduced in the liver, lungs, and kidneys in the phage treatment group. PaeP_Ls shows therapeutic potential against the MRPA1 strain of <i>P. aeruginosa</i>.IMPORTANCEThe lytic bacteriophage PaeP_Ls was isolated and thoroughly described in this study; its genomic analysis showed no virulence or resistance threats, indicating exceptional safety. More importantly, we showed that PaeP_Ls therapy effectively removed pathogens from the bloodstream, reduced organ damage, and greatly increased survival rates in a therapeutically relevant mouse sepsis model. This increases the translational development of phage therapy toward clinical application in addition to offering a novel phage option for fighting multidrug-resistant <i>Pseudomonas aeruginosa</i> infections.