Isolation and identification of a newly discovered broad-spectrum Acinetobacter baumannii phage and therapeutic validation against pan-resistant Acinetobacter baumannii.

The treatment of Acinetobacter baumannii (A. baumannii) poses significant clinical challenges due to its multidrug/pan-drug resistance. In this study, we isolated a broad-spectrum lytic A. baumannii phage, named P425, from medical wastewater, targeting nine multidrug-resistant A. baumannii (MDRAB) with diverse capsular types. Biological characterization revealed that P425 maintains activity at pH range of 3-12 and temperature range of 4-50 ​°C. It resists UV irradiation for 20 ​minutes, and had an optimal multiplicity of infection (OMOI) is 0.00001. The adsorption kinetics showed that P425 achieves > 90% within 10 ​minutes of incubation, and the one-step growth curve indicated a 10-min latent period, with a burst size of 184 ​PFU/cell. The genome sequencing results indicated that it harbors a double-stranded DNA genome of 40,583 bp with a GC content of 39.39%. Intergenomic similarity analysis classified it as a novel species within the Friunavirus genus, while electron microscopy results showed that it belongs to the Podoviridae family. Notably, P425 exhibits potent 24-h in vitro inhibitory activity against MDRAB, and demonstrates synergistic effect at an MOI of 0.001 when combined with five classes of antibiotics targeting distinct antimicrobial mechanisms. Safety evaluations confirmed the absence of cytotoxicity, hemolytic activity, or systemic toxicity both in vitro and in vivo. In mouse infection models, P425 can significantly improve the survival rates of mice infected with Ab25 (ST1791/KL101). When co-administered with levofloxacin, it achieved 100% protection against mortality and promoted immune recovery. Collectively, P425 is a prospective lytic phage that could offer novel strategies for combating MDRAB infections.