Ecology of Pseudomonas aeruginosa infections

The Gram-negative opportunistic pathogen Pseudomonas aeruginosa infects many different tissues types of immunocompromised individuals, especially the soft tissues and lungs. Despite the prevalence of P. aeruginosa in multiple infection environments, many of the mechanisms controlling this bacterium’s ability to thrive during infection remain unexplained. Therefore, I explored two facets of the ecology of P. aeruginosa infections: 1) the presence of co-infecting bacterial species and 2) the disturbance by antimicrobial treatment. The fitness-based genomic approach, Transposon sequencing (Tn-seq) was used to identify P. aeruginosa fitness determinants during chronic wound infection with the common co-infecting species, Staphylococcus aureus. The Tn-seq data revealed several genes that P. aeruginosa requires during co-infection with S. aureus. In particular, I demonstrated that the ability of P. aeruginosa to biosynthesize glutathione is a crucial determinant of P. aeruginosa fitness during chronic wound co-infection with S. aureus, potentially to relieve oxidative stress. To explore how the disturbance by antimicrobial treatment affects P. aeruginosa, I combined expression- (RNA sequencing) and fitness-based (Tn-seq) genomic techniques and identified genes involved in P. aeruginosa in vitro resistance to various antimicrobials.