A novel Queuovirinae subfamily phage targeting Acinetobacter baumannii: Isolation, characterization, and synergistic lysis system.

Abstract

BACKGROUND: Acinetobacter baumannii is a typical extensively drug-resistant Gram-negative opportunistic pathogen. Bacteriophages and their encoded lytic proteins, such as endolysins and holins, represent a promising novel therapeutic approach. METHODOLOGY: A broad-host-range lytic phage, HD01, was isolated and characterized through transmission electron microscopy, genome sequencing, and phylogenetic analysis. Its biological properties, including latent period and stability, were assessed. Therapeutic efficacy was evaluated in a Galleria mellonella infection model. The endolysin (HD01_79) and holin (HD01_80) were cloned, expressed, purified, and tested for antimicrobial activity. KEY FINDINGS: HD01 features an icosahedral head and a non-contractile long tail, and possesses a 56,791-bp dsDNA genome containing 81 ORFs. It is proposed as an unclassified monospecific genus within the Queuovirinae subfamily. The phage exhibits a short latent period, a high titer (1 × 10 PFU/mL), and stability under physiological pH and temperature conditions. In the G. mellonella model, HD01 significantly improved larval survival. The purified endolysin and holin exhibited potent, synergistic antibacterial activity against A. baumannii and clinical drug-resistant strains by hydrolyzing peptidoglycan glycosidic bonds and disrupting the membrane potential, respectively. CONCLUSION: Phage HD01 and its two-component lytic system represent a promising novel strategy for combating infections caused by drug-resistant A. baumannii.