Background: The emergence and rising of the carbapenem-resistant P. aeruginosa (CRPA) as a life-threatening pathogen has been causing serious global problems. Here, we characterized and sequenced the phage Bφ-R656 (YMC11/11/R656 PAE BP), which lyses carbapenem-resistant P. aeruginosa strains, and the efficacy of phage Bφ-R656 as an antibacterial agent candidate evaluated using a mouse infection model.

Methods: CRPA strains were collected from patients at a hospital in South Korea. Phages were isolated from sewage samples using the agar double-layered method. The phage was characterized by transmission electron microscopy, host spectrum, adsorption rate, one-step growth curve, the thermal/pH stability test, and the bacterial lysis assay. Whole genome sequencing was performed using the 454-junior genome analyzer. The therapeutic efficacy of the phage therapy was evaluated using a mouse intranasal infected model.

Results: A novel bacteriophage Bφ-R656, belonging to the family Siphoviridae, showed the high adsorption rate (~99% within 5 min), and latent period and burst size exhibited 30 min and 253 plaque forming units/infected cell, respectively. It lysed 12 of 29 CRPA clinical strains, and displayed strong lytic activities against host bacteria. Optimal storage temperature of Bφ-R656 was 4°C and exhibited stability across a broad pH range (pH 4–10) up to day 3. The genome of the Bφ-R656 has ds DNA with 60,919 bp (GC content of 58.7%) containing 113 putative open reading frames, which did not detect lysogenic or toxin-related genes.
The phage Bφ–R656 significantly improved the survival and the damage in the lung of the infected mice. Bacteria in the lung also decreased at day 5 post-infection. Furthermore, the signs of toxicity or side effects were not observed in the phage-administered group.

Conclusions: In this study, the therapeutic efficacy and safety data in vivo suggest that a novel P. aeruginosa phage Bφ-R656 has potential as an alternative antibacterial agent against CRPA infections.