Host Airway Proteins Interact with Staphylococcus aureusduring Early Pneumonia

ABSTRACTStaphylococcus aureusis a major cause of hospital-acquired pneumonia and is emerging as an important etiological agent of community-acquired pneumonia. Little is known about the specific host-pathogen interactions that occur when S. aureusfirst enters the airway. A shotgun proteomics approach was utilized to identify the airway proteins associated with S. aureusduring the first 6 h of infection. Host proteins eluted from bacteria recovered from the airways of mice 30 min or 6 h following intranasal inoculation under anesthesia were subjected to liquid chromatography and tandem mass spectrometry. A total of 513 host proteins were associated with S. aureus30 min and/or 6 h postinoculation. A majority of the identified proteins were host cytosolic proteins, suggesting that S. aureuswas rapidly internalized by phagocytes in the airway and that significant host cell lysis occurred during early infection. In addition, extracellular matrix and secreted proteins, including fibronectin, antimicrobial peptides, and complement components, were associated with S. aureusat both time points. The interaction of 12 host proteins shown to bind to S. aureusin vitro was demonstrated in vivo for the first time. The association of hemoglobin, which is thought to be the primary staphylococcal iron source during infection, with S. aureusin the airway was validated by immunoblotting. Thus, we used our recently developed S. aureuspneumonia model and shotgun proteomics to validate previous in vitro findings and to identify nearly 500 other proteins that interact with S. aureusin vivo. The data presented here provide novel insights into the host-pathogen interactions that occur when S. aureusenters the airway.