Biological characterization and stability of three lytic wastewater-derived bacteriophages targeting multidrug-resistant Acinetobacter baumannii and A. johnsonii clinical strains.

Due to the rapidly increasing problem of pathogen resistance to drugs, including bacterial resistance to antibiotics, there is a growing need to explore new therapeutic solutions. One of the multidrug-resistant pathogens responsible for many difficult-to-treat infections is Acinetobacter baumannii. The clinical relevance of another species, A. johnsonii, is also increasingly being recognized. As the development pipeline for new antibiotics remains limited, alternative antimicrobial approaches are urgently required. Among these, the therapeutic use of bacteriophages against multidrug-resistant pathogens is currently gaining renewed interest. In this study, we describe the comprehensive characterization of three novel Acinetobacter-specific bacteriophages (Acba_19, Acjo_20 and Acba_21) isolated from sewage samples. The research were conducted using clinical strains obtained from various infection sites of patients in healthcare facilities in Poland. Genomic analysis revealed no markers of temperate phages in any of the isolates, allowing their classification as strictly lytic viruses. In addition to determining basic parameters of phages - such as lytic range, species specificity, virion morphology, adsorption dynamics and infection kinetics - we also conducted stability studies of phage preparations under various conditions. These studies included assessments of pH and temperature stability, evaluation of different cryoprotectants (such as trehalose, glycerol, and pluronic), as well as the effects of storage containers made of glass and plastic materials.