With the rising prevalence of multidrug-resistant (MDR), extensively drug-resistant (XDR), and pandrug-resistant (PDR) strains of Pseudomonas aeruginosa, the development of alternative therapeutic approaches has become increasingly important. Among these, the use of bacteriophages represents a particularly promising strategy for the treatment of infections caused by multidrug-resistant pathogens.

The aim of this study was to isolate and characterize bacteriophages lytically active against P. aeruginosa, to determine their activity spectrum against clinical isolates, and to assess the potential of combining bacteriophages with antibiotics.

Materials and methods. The lytic activity of bacteriophages was tested against 23 clinical isolates of P. aeruginosa obtained from pediatric bloodstream infections, including strains carrying antibiotic resistance genes blaNDM-1, blaIMP, blaVIM, and blaTEM. Antimicrobial susceptibility of bacterial isolates was determined using the disk diffusion method according to EUCAST recommendations. Bacteriophages were isolated from wastewater samples collected in Kyiv. Lytic activity was evaluated by the Spot test and a modified agar overlay assay. Morphological characteristics were examined using transmission electron microscopy. Bacteriophage-antibiotic interactions were assessed by a modified disk diffusion method.

Results. Between 2021 and 2024, a total of 62 bacteriophages were isolated from wastewater, belonging to the Myoviridae-like, Siphoviridae-like, and Podoviridae-like morphotypes. Their lytic spectra varied considerably, ranging from narrow specificity (2–4 strains) to the ability to lyse more than 20 clinical bacterial isolates. Overall, 29.0 % of bacteriophages showed activity against multiple strains, and some isolates exhibited a broad host range, with specific lysis observed in up to 91.3 % of tested strains. Combination testing revealed a predominantly synergistic interaction between bacteriophages and β-lactam antibiotics, manifested by an increase in both plaque size and number.

Conclusions. The isolated bacteriophages demonstrated substantial variability in lytic activity and have potential applications in the treatment of infections caused by multidrug-resistant P. aeruginosa strains. The findings support the feasibility of establishing bacteriophage collections and applying combined bacteriophage-antibiotic therapies. Considering the current epidemiological situation in Ukraine, these results are of practical importance for the development of new antimicrobial strategies.