In vitro, genomic characterization and pre-clinical evaluation of a new thermostable lytic Obolenskvirus phage formulated as a hydrogel against carbapenem-resistant Acinetobacter baumannii.

The urgent threat of carbapenem-resistant Acinetobacter baumannii (CRAB) necessitates the development of new antimicrobial strategies. Bacteriophage (phage) therapy is one of the most promising alternative strategies that can be implemented to combat multidrug-resistant (MDR) bacterial infections. Herein, an A. baumannii phage VB_AB_Acb75 that exhibited lytic activity against 6 CRAB isolates (21.43%) with stability at up to 70 °C, pH 2-12, and high concentrations of organic solvents was isolated and characterized. The transmission electron microscope (TEM) detected a tailed phage with an icosahedral head and contractile tail (myoviral morphotype). The Oxford nanopore sequencing results showed an A. baumannii phage genome size of 45,487 bp, a G + C content of 38%, and 42 open reading frames (ORFs). The phylogenetic analysis, ORF, and TEM analysis indicated that A. baumannii phage VB_AB_Acb75 belongs to a novel species in the Obolenskvirus genus. Furthermore, the phage-loaded Carbopol 940 hydrogel was preclinically evaluated for wound healing effectiveness in the burn-wound animal model infected with the CRAB isolate. The histology findings showed a marked improvement in wound healing through a thick epidermal layer and the formation of well-organized fibrous connective tissue covered by a scab at the site of injury, as well as the ability to eliminate CRAB infection, as compared to the control group. In conclusion, based on in vitro, physicochemical properties, and preclinical findings, the phage-loaded hydrogel is expected to be a promising candidate for clinical evaluation against CRAB-associated skin infections.