Assessment of quorum quenching enzymes as an eradication strategy against Pseudomonas aeruginosa biofilms

Details

Supervisors

Gillis, Annika

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

enPseudomonas aeruginosa is an opportunistic pathogen well known for its ability to form biofilms and regulate virulence through quorum sensing mechanisms. These properties contribute to its persistence in clinical and food-processing environments and complicate its eradication using conventional antimicrobial strategies. In this context, quorum quenching approaches, which aim to interfere with bacterial communication rather than antibacterial effect, are increasingly studied as promising antivirulence alternatives. The aim of this master’s thesis is to evaluate the potential quorum quenching activity of Bacillus strains against P. aeruginosa. More specifically, the work focuses on the ability of Bacillus cell-free supernatants to interfere with quorum sensing-regulated phenotypes such as biofilm formation. To achieve this objective, several experimental approaches were implemented and optimized in order to obtain reproducible and reliable assay conditions. Biosensor assays based on Chromobacterium subtsugae CV026 were performed to detect potential AHL degradation activities, while violacein quantification assays and biofilm formation experiments were carried out to evaluate the impact of Bacillus supernatants on quorum sensing-related phenotypes. In parallel, seven P. aeruginosa strains originating from the MIAE collection were characterized for virulence-related phenotypes including pyocyanin production, hemolytic activity, DNase activity and biofilm formation capacity. The main outcomes of this work are that several Bacillus supernatants (Bacillus thuringiensis T10A001, T24 001 and T30 001 and Bacillus cereus AH545) produced visible violacein synthesis inhibition in biosensor assays, suggesting a potential quorum quenching activity. Biofilm quantification experiments also revealed strain-dependent effects, with some supernatants (B. thuringiensis T24A001, HD1 and 4L1) reducing biofilm formation in specific P. aeruginosa strains (PAO1, SI0271 and SI0086). Importantly, no bacterial growth inhibition was observed during the experiments, supporting an antivirulence rather than antibacterial mode of action. However, violacein quantification assays produced variable and non-significant results under the tested conditions, highlighting the complexity of studying quorum quenching mechanisms and the importance of protocol optimization. Overall, this master’s thesis contributes to the exploration of quorum quenching strategies as complementary approaches to limit P. aeruginosa biofilm formation. The work also highlights several perspectives for future studies, notably the further characterization of Bacillus quorum quenching compounds and the evaluation of their effects under conditions more representative of industrial environments.