Microbiological rationale for alternative strategies to combat infections causedby antibiotic-resistant Pseudomonas aeruginosa

This study aimed to investigate the activity of the drug Pyofag against clinical isolates ofPseudomonas aeruginosa and to evaluate the effectiveness of the combined action of surface-activeantiseptics and bacteriophages. To achieve this aim, classical methods for the isolation andidentification of bacteria were employed. Antibiotic susceptibility of Pseudomonas isolates was determined using the disc diffusion method, while susceptibility to surface-active antiseptics(decamethoxine, benzalkonium chloride, chlorhexidine bigluconate, octenidine dihydrochloride, andpolyhexanide) was assessed using the broth dilution method. The susceptibility of clinical isolates toPyofag was evaluated based on the optical density of bacterial suspensions after 18 hours ofincubation with the preparation. The nature of the combined effect of bacteriophages and antisepticson P. aeruginosa was assessed by calculating the lytic index of the phage on planktonic bacterialforms cultured in media containing sub-bacteriostatic concentrations of antiseptics. The resultsshowed that all 54 isolated clinical strains of P. aeruginosa retained high susceptibility only to reserveantibiotics – colistin (94.4%) and cefiderocol (75.9%). Resistance to other antipseudomonalantibiotics (cefepime, ceftazidime, piperacillin-tazobactam, imipenem, and ciprofloxacin) wasobserved in 96.3%-100% of isolates. However, aminoglycosides (gentamicin, tobramycin, amikacin)and meropenem remained effective against 29.6%-44.4% of strains. Antiseptic agents containingsurface-active compounds demonstrate strong antipseudomonal properties and are capable ofinhibiting bacterial proliferation at concentrations ranging from 16.4-22.5 μg/mL (octenidinedihydrochloride, decamethoxine, chlorhexidine bigluconate) to 65-145.7 μg/mL (polyhexanide,benzalkonium chloride). It was confirmed that decamethoxine, octenidine, and chlorhexidine exhibitsignificantly greater antibacterial activity than polyhexanide and benzalkonium chloride (p < 0.01).The isolated Pseudomonas strains showed high susceptibility to the pharmaceutical preparationPyofag: the lytic activity index (Is) of Pyofag exceeded 0.5 in 70.4% of strains, indicating that 50%of the bacterial population was destroyed during the dynamic interaction between bacterial growthand phage replication. In media containing sub-bacteriostatic concentrations of decamethoxine,chlorhexidine, or octenidine, both susceptible (n = 7, Is = 0.69) and resistant (n = 8, Is = 0.15) strainswere lysed more intensively by the bacteriophage. This was evidenced by an increase in thesusceptibility index to 0.80-0.87 in susceptible strains and to 0.54-0.70 in phage-resistant strains,respectively