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Mataigne_03371500_2020.pdf
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- Antibiotic resistance emergence and spreading represent a worldwide growing health threat, especially among human and animal pathogenic bacteria, because they can lead to non-treatable infections. As a result of the antibiotic use in livestock, antibiotic residues, antibiotic resistant bacteria and antibiotic resistant genes end up in manure. They are likely to spread to agricultural soil after manure application on fields. Antibiotic resistance genes found on mobile genetic elements are able to easily spread in the environment. In fact, plasmid-mediated horizontal gene transfer is considered as a major driving force of antibiotic resistant genes. In this context, this master thesis aimed to set up bacterial triparental mating conjugation systems able to isolate environmental plasmids potentially associated with antibiotic resistance genes. For this purpose, and to enlarge the possibility of capturing environmental plasmids, two conjugations systems have been developed: a Gram-positive system based on Bacillus thuringiensis sv. israelensis strains and a Gram-negative system based on Escherichia coli strains. This study aimed also to establish a protocol using these same systems in order to study the influence of the complex soil and manure matrices on the transfer and mobilization rates of different known plasmids. The conjugation system transfer frequencies were calculated in optimal growth conditions. The obtained transfer frequencies values ensured that the conjugation systems were operative and ready to be used in further evaluation of environmental matrices influence on conjugation. The conjugation capture systems pretests in environmental matrices started with soil and compost samples harvested in Louvain-la-Neuve. These pretests allowed improvements of the conjugative capture systems and of the matrix influence protocol. They permitted to highlight difficulties that could be encountered when the systems will be applied to agricultural soil and manure samples from Belgian farms.