Determining the Injury-Associated Microbial Nutrients that Facilitate Secondary Bacterial Infection in Acutely Injured Lungs

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PROJECT SUMMARY Secondary pneumonia occurs frequently in patients with acutely injured lungs and increases the mortality of acute lung injury. Although acute lung injury is caused by a variety of pulmonary and systemic insults, all etiologies of acute lung injury result in compromised integrity of the blood-air barrier, allowing an influx of protein- rich, serum-derived fluid in the pulmonary airspace. Consequently, the microenvironment within acutely injured lungs is radically altered from health and provides a selective advantage to the outgrowth of pneumonia- associated pathogens. However, the factors that enable bacterial growth in acutely injured lungs are unknown. The objective of this study is to determine which soluble factors in the injured lung enhance the survival of pneumonia-associated bacteria by serving as bacterial nutrients. Using the proposed research plan, we will test the central hypothesis that the influx of serum-derived edema into the injured lung microenvironment increases the diversity and quantity of substrates which can be taken up and metabolized by pneumonia- associated bacteria, enhancing bacterial growth and fitness in the injured lung microenvironment. We will test this hypothesis through the following specific aims: (1) determine the bacterial nutrient uptake systems and metabolic pathways that provide fitness advantages for pneumonia-associated bacteria in the injured lung microenvironment, and (2) determine the diversity and quantity of bacterial nutrient substrates that become available in the injured lung microenvironment and enhance bacterial growth. To accomplish these specific aims, we will employ Pseudomonas aeruginosa and Staphylococcus aureus, two of the most common pneumonia- associated pathogens, along with a murine model of oxygen-induced lung injury and a novel ex vivo culture system to compare differences in bacterial growth and gene expression between healthy and injured lung microenvironments. To complement the murine modeling and ex vivo bacterial culture, we will perform targeted metabolite analysis to detect the presence of host-derived nutrients that support bacterial growth in injured lungs. We will use bacterial knockouts, competitive co-culture, and in vitro nutrient modulation experiments to validate our findings. This study will identify specific, injury-associated nutrients that directly promote bacterial growth in acutely injured lungs and establish the influence of nutrient availability on the progression from respiratory dysbiosis to secondary bacterial infection in the context of acute lung injury. Furthermore, the results of this study will provide a mechanistic basis for the development of clinical interventions for patients with acute lung injury at risk for pneumonia. Successful completion of the proposed research and training plan will enable Ms. Baker to develop professional skills pertaining to communication and leadership and unique interdisciplinary expertise in pulmonary pathobiology, bacterial pathogenesis, and bioinformatics. This F31 award will be essential for her continued professional and scientific development and will equip her for the next step of her professional journey to become an independent academic researcher in the field of pulmonary host-microbiome interactions.