(362f) Metabolic Modeling of Interactions Between Pseudomonas aeruginosa and Staphylococcus aureus in Cystic Fibrosis Biofilm Infections

Pseudomonas aeruginosa and Staphylococcus aureus are two bacteria most commonly isolated from the lung infections of cystic fibrosis (CF) patients. Individuals co-infected with these two bacteria are more prone to exacerbations and hospitalization than patients infected with either bacterium alone; thus, such coinfections contribute to worse clinical outcomes in this patient population. CF infections are often characterized by the formation of biofilms in which bacteria reside in a protective matrix of self-produced polymers. More effective treatment strategies are needed for these polybacterial biofilm infections to improve the quality of life and reduce mortality in CF patients. We hypothesize that interactions between these two bacteria are attributable to metabolites that are secreted by each species and diffuse over long distances to shape spatial biofilm structure. Our in vitro studies show that S. aureus shifts from respiratory to fermentative metabolism in the presence of P. aeruginosa supernatant, resulting from inhibition of the S. aureus electron transport chain (ETC) by siderophores and 2-heptyl-4-hydroxy quinoline-N-oxide (HQNO). Moreover, we observed that S. aureus is more tolerant to the antibiotics when grown in the presence of P. aeruginosa supernatant.

In this study, we developed a multispecies biofilm metabolic model to further investigate the hypothesis that P. aeruginosa can exert its influence on S. aureus at a distance via secreted factors. Simulations were performed by supplying glucose, amino acids and oxygen at the top of the biofilm to mimic the in vivo CF environment. P. aeruginosa was forced to secrete HQNO, which diffused through the biofilm and inhibited S. aureus ETC through cytochrome b. Lactate synthesized by S. aureus was modeled to be the preferred carbon source for P. aeruginosa, as has been shown experimentally. The multispecies biofilm model was shown to reproduce experimentally observed behavior, including dominance of P. aeruginosa, upregulation of S. aureus fermentative metabolism and enhanced P. aeruginosa growth due to lactate cross feeding. These results represent the first step towards integrating laboratory experiments with clinically isolated bacterial strains and in silico modeling of biofilm metabolism to unravel the enhanced pathogenicity of this CF coinfection.