DISSECTION OF P. AERUGINOSA / HOST INTERACTION DURING ACUTE AND CHRONIC AIRWAYS INFECTION

Cystic fibrosis (CF) lung disease is characterized by transient airway P. aeruginosa infections and excessive neutrophil-dominated inflammation early in life followed by permanent chronic infection leading to the decline in lung functions. In CF disease, strong selective pressures in the airways lead to P. aeruginosa genotypic and phenotypic adaptation. Thus, colonization is maintained by P. aeruginosa pathoadaptive lineages, which are clonal with the initially acquired strain. The main aim of this thesis is to dissect the strategies through which the P. aeruginosa patho-adaptive strains interact with the host causing persistence and damage. Comparing sequential strains isolated from a CF patient, including mucoid and non-mucoid phenotypes, isolated during a period of up to 7.5 years, we found that P. aeruginosa is subjected to lipid A and peptidoglycan modification as a strategy to evade the innate immune response. Next, virulence of whole bacterial cells including P. aeruginosa early and late adapted clonal isolates were tested in human CF bronchial epithelial cells IB3-1 by macroarray analysis and ELISA. P. aeruginosa early strains induced a stronger inflammatory response in comparison to late strains, while late strains up-regulated MMP-9, liable for tissue damage. When we tested host response in two murine models of acute and chronic pneumonia, we found that P. aeruginosa early strain was virulent and lethal. Although attenuated in acute virulence and mortality, late adapted isolates retained their capacity to persist in mouse models of chronic infection up to 90 days with a stable bacterial load in the lung. P. aeruginosa early strain induced a higher proinflammatory response in the acute phase of infection in terms of cytokines and chemokines (MIP-2, KC, IL-6, IL-1β MIP-1α), but chronic colonization with late adapted isolates sustained mainly cytokines involved in lymphocytes recruitment and in tissue remodelling and damage (TNF-α, IL-17a, IFN-γ, MCP-1, TGF-β1). In addition, histological examination of murine lungs following both acute and chronic infection showed that late adapted isolates modulated host response increasing numbers of mucin-positive goblet cells, collagen deposition and apoptotic cells, typical hallmarks of damage in the airway chronic diseases. Our findings suggest that P. aeruginosa patho-adaptive variants, although attenuated in acute virulence, can promote persistence while causing tissue damage and fibrosis in the airways.