Longitudinal Analysis of Lung Microbiome, Immune Response, and Metabolism in Ventilator-Associated Pneumonia: A Cohort Study.

Rationale: Ventilator-associated pneumonia (VAP) is a common complication in patients under invasive mechanical ventilation (IMV), yet its underlying mechanisms remain poorly understood. This study investigated the lung microbiome, inflammatory response, and metabolism in patients undergoing IMV to identify factors that may predispose them to developing VAP. Objectives: To investigate how changes in lung microbiome composition, inflammatory response, and metabolic profiles may predispose patients undergoing IMV to develop VAP. Methods: Patients requiring IMV for at least 48 hours due to non-infectious respiratory failure were enrolled. Bronchoalveolar lavage (BAL) samples were collected at baseline, upon VAP diagnosis, or after 72 hours for non-VAP cases. DNA sequencing, cytokine quantification, and metabolomic analyses were performed. Results: Of the 80 patients, 41 (51%) developed VAP. No significant differences in alpha or beta diversity of the lung microbiome were observed between groups. However, both groups showed changes in microbiome composition over time, suggesting an impact of IMV. TNF-α lung levels were significantly higher in VAP patients, while lung IL-1β increased in all patients. Metabolomic analysis revealed shifts in pentose phosphate and citric acid cycle pathways, indicating a transition to anaerobic metabolism in the lungs of VAP patients. Conclusions: Mechanical ventilation drives dynamic changes in the lung microbiome, independent of VAP development. Lung inflammation with elevated TNF-α was documented in VAP, while IL-1β reflected the broader effects of IMV. Finally, metabolic evidence of anaerobic adaptation in the lungs of patients with VAP was observed.