Inhibition of Human Inflammatory Responses by Methicillin Resistant Staphylococcus aureus (MRSA)

Alexander Parks, Jennifer Dankoff, Kyler Pallister, Dr. Tyler Nygaard, and Dr. Jovanka Voyich, Department of Microbiology and Immunology, Montana State University, 109 Lewis Hall, Bozeman MT 59717

Methicillin resistant Staphylococcus aureus (MRSA) is a common human pathogen that causes a wide range of diseases and is known to be able to evade killing by human neutrophils. The SaeR/S two component system of S. aureus controls secretion of proteins that disrupt neutrophil function. It has been previously demonstrated that suppression of the NF-κB inflammatory pathway is linked to SaeR/S through an unknown mechanism. In the current study, we investigate the hypothesis that inhibition of the pro-inflammatory NF-κB pathway in human neutrophils is due to a SaeR/S-regulated secreted factor. To assess the inhibitory effects of SaeR/S secreted proteins, human blood was inoculated with filtered (0.2µm) supernatant from overnight cultures of both wild-type (USA300) and isogenic mutant strains including: ΔsaeR/S, Δagr, and knockouts of select toxins regulated by SaeR/S. Ongoing experiments are investigating NF-κB activity in neutrophils using an anti-NF-κB antibody (NF-κB p65) and activity is being evaluated using flow cytometry. Preliminary studies indicate a secreted factor regulated by SaeR/S, and not Agr, reduces NF-κB activity by ~40%.  This activity is no longer seen when supernatant undergoes protein digestion with Proteinase K, indicating the secreted factor is a protein. This trend of SaeR/S-mediated NF-κB repression is conserved between two clinically relevant S. aureus strains, USA300 and USA400. Additional experiments are ongoing using methods to measure membrane permeability, size exclusion assays, and a comparison of additional clinically relevant strains to assess conservation of this protein. In conclusion, the inhibition of NF-κB signaling pathways in neutrophils is caused by a SaeR/S mediated protein. Future work includes identifying the gene coding for this inhibitory protein and generating a knockout strain to confirm it. Identifying the mechanism behind NF-κB inhibition could provide novel MRSA treatment options as well as therapeutics for inflammatory disorders.

Additional Abstract Information

Presenter: Alexander Parks

Institution: Montana State University Bozeman

Type: Poster

Subject: Microbiology

Status: Approved

Time and Location

Session: Poster 8
Date/Time: Tue 5:00pm-6:00pm
Session Number: 5631