Project description:Clinical case studies have reported that the combined use of specific lytic phage(s) and antibiotics reduces the severity of difficult-to-treat Pseudomonas aeruginosa infections in many patients. In vitro methods that attempt to reproduce specific pathophysiological conditions can provide a reliable assessment of the antibacterial effects of phages. Here, we measured bacterial killing kinetics and individual phage replication in different growth phases, including biofilms, elucidating factors influencing the efficacy of two phages against the laboratory strain P. aeruginosa PAO1. While two-phage combination treatment effectively eliminated P. aeruginosa in routine broth and in infected human lung cell cultures, the emergence of phage-resistant variants occurred under both conditions. Phage combination displayed initial inhibition of biofilm dispersal, but sustained control was achieved only with a combination of phages and meropenem. In contrast, surface-attached biofilm exhibited tolerance to phage and/or meropenem, suggesting a spatiotemporal variation in antibacterial effect. Moreover, the phage with the shorter lysis time killed P. aeruginosa more rapidly, selecting a specific nucleotide polymorphism that likely conferred a competitive disadvantage and cross resistance to the second phage of the combination. These findings highlight biofilm developmental phase, inter-phage competition and phage resistance as factors limiting the in vitro efficacy of a phage combination. However, their precise impact on the outcome of phage therapy remains uncertain, necessitating validation through phage efficacy trials in order to establish clearer correlations between laboratory assessments and clinical results.
