Streptococcus mitis Downregulates Pseudomonas aeruginosa Quorum Sensing and Virulence Expression in Pairwise Interaction Model
Stuart, Matera L.
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Cystic fibrosis (CF) is a respiratory genetic disorder that increases lung susceptibility to infection. Most CF lung infections contain Pseudomonas aeruginosa and Streptococcus mitis bacteria, which are drug resistant pathogens that co-exist together in CF lung biofilm. However, limited information exists on their in vitro pairwise interaction and the dynamics of their quorum sensing (QS) and virulence factor expressions. In this study, a colony forming unit (CFU) protocol was conducted to estimate the total number of bacteria present in 1mLof an overnight mixture, along with measurements of P. aeruginosa virulence expression of las B protease using a bio-reporter luciferase (lux) fusion in microaerophilic and aerobic conditions. They were also tested in aerobic four hour bacterium pre-treatment trial conditions to understand initial growth effects on QS. The results indicated that the P. aeruginosa CFUs in pairwise samples of S. mitis formed significantly lower CFUs in microaerophilic conditions than aerobic, indicating that P. aeruginosa environmental stabilization favored aerobic conditions. In addition, P. aeruginosa las B. lux virulence expression was significantly downregulated in the presence of S. mitis in aerobic conditions. Future studies should determine if S. mitis downregulates las B. lux expression via chemical pH changes in comparison to a buffer stabilization media. The S. mitis pH change may be responsible for denaturing AHL signal molecules necessary for P. aeruginosa las B. lux activation. Artificial sputum medium (ASM) could also be applied to future studies to determine how lux expression and QS regulated growth are impacted in near-CF lung conditions.