Characterization of a lytic phage and its efficacy against carbapenem-resistant Pseudomonas aeruginosa infection in mice

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Carbapenem-resistant Pseudomonas aeruginosa (CRPA) has emerged as a significant global public health threat due to its increasing prevalence and dissemination, necessitating the development of novel antimicrobial agents. In this regard, bacteriophages, particularly lytic phages, offer a promising alternative to conventional antibiotics for the treatment of such resistant infections. In this study, we isolated and characterized a lytic Pseudomonas phage, Pa_WF01, from hospital sewage, which specifically targets clinical CRPA strains. The host range, multiplicity of infection (MOI), morphology, one-step growth curve, thermal and pH stability, chloroform sensitivity, and lytic activity of Pa_WF01 were evaluated. Our findings showed that the MOI, latent period, and burst size of Pa_WF01 were approximately 0.0001, 10 min, and 154 phages per cell, respectively. Furthermore, Pa_WF01 exhibited robust lytic activity across a broad range of pH values (4-12) and temperatures (4-50 °C), effectively inhibiting bacterial growth. Transmission electron microscopy (TEM) analysis supported that Pa_WF01 exhibits morphological characteristics similarity to the Schitoviridae family, and the result was further confirmed by phylogenetic analysis of complete genome sequences. Whole-genome sequencing revealed that Pa_WF01 has a double-stranded DNA genome of 73,369 bp and a GC content of 54.78%, containing 94 open reading frames (ORFs). Notably, no tRNA, virulence, or antibiotic resistance genes were identified within the genome. Phylogenetic tree analysis further classified Pa_WF01 as closely related to phages of the Litunavirus genus. In vivo, Pa_WF01 significantly improved the survival rate of mice infected with CRPA, reduced inflammatory responses, decreased bacterial loads in organs (lung, liver, and spleen), and alleviated organ damage. Additionally, in vitro analysis demonstrated that Pa_WF01 enhanced serum-mediated bactericidal activity. Taken together, these results highlight the potential of phage Pa_WF01 as a viable therapeutic alternative for treating CRPA infections in clinical practice.

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