Pseudomonas aeruginosa Promotes the Survival of Strict Anaerobic Pathogens Under Aerobic Growth Conditions

The cystic fibrosis (CF) airway is characteristically colonized with a mucoid Pseudomonas aeruginosa infection that is associated with high morbidity and mortality. Recent evidence also supports a role for strict anaerobes such as Porphyromonas gingivalis and Fusobacterium nucleatum as pathogens in the CF airway. These bacteria lack the antioxidant enzymes such as peroxidases, superoxide dismutases and catalases necessary to survive exposure to the reactive oxygen species encountered in the inflamed CF airway environment. Because of this, it is unclear how they can establish an infection in the CF airway. It is the hypothesis of these studies that P. aeruginosa may facilitate the growth of strict anaerobes through metabolic reduction of oxygen in the sequestering environment created by the extracellular polymers associated with mucoid P. aeruginosa. To test this, we performed a series of broth and agar co-cultures of strains of P. aeruginosa, F. nucleatum, and P. gingivalis in various combinations of growth conditions, including assorted oxygen levels. We determined that F. nucleatum and P. gingivalis require the presence of P. aeruginosa to grow in an aerobic atmosphere. Both strains of P. aeruginosa tested were able to facilitate a significantly greater recovery of anaerobic organisms in broth culture and on agar plates after prolonged exposure to oxygen than the anaerobes produced alone. The protective effects by P. aeruginosa on the anaerobic bacteria may be due to a combination of its use of oxygen in a microenvironment and its formation of a physical barrier around the anaerobic bacteria. Further experimentation must be performed to determine the exact protective functions. The implications of this research could be used in the future to help develop treatments targeting the protective mechanisms to reduce disease in CF hosts.Bachelor of Scienc