Étude de la virulence et de la formation de biofilms chez Pseudomonas aeruginosa

Authors: Gagné-Thivierge, Cynthia
Advisor: Charette, SteveLévesque, Roger C.
Abstract: Pseudomonas aeruginosa is an opportunistic bacterial pathogen known to cause chronic lung infections in cystic fibrosis (CF) patients. Some strains, adapted to the CF lung microenvironment, show distinguishing phenotypes such as an increased resistance to antibiotic treatments and an enhanced biofilm formation. The study of P. aeruginosa isolates from CF patients is necessary to understand the genetic determinants explaining this adaptation and to allow the development of new ways to fight this bacterium. A library of LESB58 mutants has been created in 2009. LESB58 is an epidemic strain among CF patients. In the study presented here, a sequential screening in three different hosts has been performed, leading to the identification of a mutant with a strong virulence defect: the STM PALES_11731 mutant. This mutant, contrary to the wild type, was unable to form biofilm-like structures (BLSs), a type of bacterial aggregation resembling biofilm, but floating in the culture medium. To assess this phenomenon among P. aeruginosa strains, the formation of adhered biofilm and BLSs in LESB58 and three other strains (the reference strain PAO1 and two environmental strains, PPF-1 and Urg-7) was compared using a novel image analysis quantification approach. The impact of the addition of divalent cations on the formation of those structures was also assessed. The results obtained demonstrate some diversity of biofilm and BLS formation in this bacterial species. They also reveal a lack of correlation between the BLS and adhered biofilm formation response to the ion treatment, suggesting that these two phenomena might not be directly related and raising questions about the mechanisms of BLS formation. The results of this project indicate that BLSs could play a role in the virulence of P. aeruginosa in CF patients and highlight the importance, in a future study, of studying the molecular and physical mechanisms responsible for their formation.
Document Type: Mémoire de maîtrise
Issue Date: 2018
Open Access Date: 8 June 2018
Permalink: http://hdl.handle.net/20.500.11794/30007
Grantor: Université Laval
Collection:Thèses et mémoires

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