Abstract The emergence of antimicrobial resistance in Pseudomonas aeruginosa has made the treatment of pneumonia increasingly difficult. Bacteriophages offer a narrow-spectrum, self-replicating alternative to antibiotics. We evaluated the therapeutic and tissue-protective effects of a three-phage cocktail against acute P. aeruginosa infection in mice.C57BL/6 mice were infected intratracheally with 1 × 108 CFU of P. aeruginosa PAO1. Two hours later, animals received 50 µL of a phage cocktail containing PSA7, PSA16, and PSA39 (1.5 x 107 PFU/mouse, MOI ≈ 0.15) via intratracheal instillation. Five-fold (3 x 106 PFU/mouse, MOI ≈ 0.03) and ten-fold (1.5 x 106 PFU/mouse, MOI ≈ 0.015) dilutions of the original phage cocktail were further tested to assess dose response. Survival, bacterial load in bronchoalveolar lavage (BAL) and lung tissue, cytokine mRNA levels, immune-cell profiles, and lung histology were examined at day 2 and day 5 post-infection.All phage-treated mice survived and recovered quickly through day 5 of the experiment, whereas most PBS-treated controls without phage cocktail died within 36 hours (p 0.0001). Phage therapy reduced bacterial counts by 3-4 log10 CFU and lowered the expression of IL-1β, IL-6, TNF-α, CXCL10, and CCL12 to baseline levels. Flow cytometry showed decreased neutrophil activation and altered macrophage and T-cell composition.Histological analysis revealed severe alveolar consolidation, hemorrhage, and dense peribronchial infiltration in PBS-treated lungs. Phage-treated lungs showed clear, dose-dependent protection. Even at low phage doses (MOI ≈ 0.03-0.015), alveolar structures were mostly preserved. Airspaces remained open with mild perivascular and peribronchial inflammation. The high phage dose group (MOI ≈ 0.15) displayed minimal exudate and nearly normal alveolar morphology. The infected mice with phage cocktail therapy displayed full recovery of tissue damage, and histology scoring confirmed a significant reduction in tissue injury compared with PBS controls (p 0.0001).The three-phage cocktail rapidly reduced bacterial burden and prevented secondary tissue damage. Inflammatory infiltration was limited, and all phage groups maintained the overall lung architecture, even at the lowest phage cocktail dose (MOI ≈ 0.015). These findings suggest that phage therapy achieves high antibacterial potency with effective tissue protection. The results support its potential use as an effective approach for treating P. aeruginosa pneumonia. This abstract is funded by: R01-AI176537, R01-AI133351
Lu et al. (Fri,) studied this question.