Molecular basis of host responses in ventilator associate pneumonia
Ventilator associated pneumonia (VAP) is the second most common hospital acquired infection (HAI) in the United States. With more than 300,000 cases annually, VAP accounts for 60% of all HAI fatalities. Current VAP diagnosis is typically based on the clinical pulmonary infection score (CPIS). The CPIS score is mostly based on recorded clinical symptoms and does not include any molecular testing. Thus, CPIS has moderate sensitivity and selectivity that leads to missed episodes, and delayed and non-specific VAP treatments. Inaccurate diagnosis impacts the naturally occurring host microbial population by applying selective pressure towards multi-drug resistant pathogens. A deeper understanding of the VAP host response mechanism towards pathogen infection will aid in early diagnosis and better therapeutic alignment. Our study was conducted on 16 intubated patients throughout their stay in the Intensive Care Unit. Endotracheal aspirates (ETA), bronchoalveolar lavage fluid (BALF), and plasma were collected at multiple time points for each patient. These samples were analyzed using shotgun proteomics involving in-gel trypsin digestion followed by liquid chromatography-mass spectrometry (LC-MS). In addition, 188 metabolites were absolutely quantitated against isotopically labeled synthetic standards using a LC-MS based targeted metabolomic assay. Our preliminary findings show 84% of identified proteins in ETA correlate to BALF, and 393 additional unique proteins were identified specifically in ETA. Gene expression analysis revealed 85% overlap of defense/immune related activity between ETA and BALF, indicating ETA as a viable and accessible alternative for monitoring disease progression and host pathogen response. A complex microbial environment modulates the host pathogen response, and 16s RNA sequencing identified shifts in dominant populations over time potentially as a result of early, poorly aligned antibiotic treatment. Our findings pave the way for the development of early detection methods of pneumonia infection and progression to provide valuable insight into pathogen specific therapeutic options.