A Newly Discovered Obolenskvirus Phage with Sustained Lytic Activity Against Multidrug-Resistant Acinetobacter baumannii.

Background: Acinetobacter baumannii is a highly concerning pathogen in hospital settings, responsible for severe infections such as ventilator-associated pneumonia, urinary tract infections, and meningitis. Its remarkable genetic plasticity facilitates the rapid acquisition of antibiotic resistance, significantly complicating treatment and increasing mortality rates. As multidrug-resistant (MDR) infections continue to rise, phage therapy emerges as a viable alternative. Methods: This study reports the isolation and characterization of Acinetobacter phage vB_AbaM_A72 from stagnant water in Jalisco, Mexico. Results: Transmission electron microscopy revealed a myovirus-like morphology with an icosahedral head (91.32 ± 0.12 nm) and a contractile tail (123.77 ± 0.19 nm). The phage exhibited high environmental resilience, tolerating temperatures up to 60 °C and pH ranging from 5 to 11. Notably, A72 demonstrated a narrow host range but effectively inhibited the growth of an MDR A. baumannii strain for at least 12 h across different multiplicities of infection. Whole-genome sequencing confirmed the absence of virulence, antibiotic resistance, or lysogeny-associated genes. Comparative genomic analysis identified A72 as the first member of a newly described Obolenskvirus species, sharing only 76.4% similarity with its closest relatives. Conclusions: These findings underscore the importance of fully characterizing novel bacteriophages to expand therapeutic libraries and reinforce the feasibility of phage therapy as a promising approach against MDR A. baumannii infections.