In vivo application of bacteriophage as a potential therapeutic agent to control OXA-66-like carbapenemase-producing acinetobacter baumannii strains belonging to sequence type 357

The increasing prevalence of carbapenem-resistant Acinetobacter baumannii (CRAB) strains in intensive care units has caused major problems in public health worldwide. Our aim was to determine whether this phage could be used as an alternative therapeutic agent against multidrug-resistant bacterial strains, specifically CRAB clinical isolates, using a mouse model. Ten bacteriophages that caused lysis in CRAB strains, including blaOXA-66-like genes, were isolated. YMC13/01/C62 ABA BP (phage Bφ-C62), which showed the strongest lysis activity, was chosen for further study by transmission electron microscopy (TEM), host range test, one-step growth and phage adsorption rate, thermal and pH stability, bacteriolytic activity test, genome sequencing and bioinformatics analysis, and therapeutic effect of phage using a mouse intranasal infection model. The phage Bφ-C62 displayed high stability at various temperatures and pH values and strong cell lysis activity in vitro. The phage Bφ-C62 genome has a double- stranded linear DNA with a length of 44,844 bp, and known virulence genes were not identified in silico. In vivo study showed that all mice treated with phage Bφ-C62 survived after intranasal bacterial challenge. Bacterial clearance in the lung was observed within 3 days after bacterial challenge, and histologic damage also improved significantly; moreover, no side effects were observed.