Isolation and characterization of two novel phages with lytic activity against multidrug-resistant Acinetobacter baumannii strains: potential for phage therapy.

The emergence of multidrug-resistant Acinetobacter baumannii (MDR-AB) has raised concerns regarding the lack of effective treatment options, prompting interest in phage therapy. In this study, two phages, designated vB_MZM_2AB-P and vB_MZM_4AB-P, were isolated and characterized for their lytic activity against MDR-AB strains. vB_MZM_2AB-P demonstrated considerable stability, retaining activity at 70 °C and pH 11.00, with over 37.10% survival rate after three months of storage. It displayed a 10-min latent period and a burst size of 39.72 PFU/cell. vB_MZM_4AB-P was stable at 50 °C and pH 7.00, but lost activity after three months of storage. Its latent period was also 10 min, with a burst size as high as 746.70 PFU/cell. Transmission electron microscopy revealed that phage vB_MZM_2AB-P has an icosahedral head with a diameter of 55.00 nm and a non-contractile tail that is 121.00 nm long, while phage vB_MZM_4AB-P has an icosahedral head with a diameter of 75.36 nm and a non-contractile tail that is 19.44 nm long. Genomic analysis showed that vB_MZM_2AB-P (43,664 bp) shared 94.18% and 92.80% similarity with phages DMU1 and SH-Ab15497, respectively, while vB_MZM_4AB-P (42,975 bp) shared 73.82% similarity with phage vB_AbaP_Acibel007. Phylogenetic analysis indicated that vB_MZM_2AB-P may represent a new genus within the order Caudoviricetes, and vB_MZM_4AB-P a new species within the genus Daemvirus. No antibiotic resistance or virulence genes were detected. These findings demonstrate that vB_MZM_2AB-P and vB_MZM_4AB-P are novel phages with distinct genomic features and favorable lytic activity against MDR-AB strains, highlighting their value for expanding phage diversity and for future fundamental research.