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RESEARCH PRODUCT

Persistance et adaptation de Listeria monocytogenes dans le sol : rôle du système de communication Agr

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Listeria monocytogenes is a ubiquitous bacterium responsible for listeriosis, a food-borne disease. This pathog•en has been isolated from varions environments of which the telluric environment. The presence of L. monocytogenes in soi! can increase health hazards due to the risk of transfer to vegetables, animais and animal products and water. Considering the role of soil in the circulation of pathogens from fann environment to plant and animal products and eventually to foodstuff, it is critical to identify intrinsic and extrinsic factors that drive the fate of L. monocytogenes in soi!. Genome-wide and transcriptomic analyses found that an important part of the genome of L. monocytogenes (7.3%) is dedicated to regulation including 209 transcriptional regulators. Among these, AgrA is the response regulator of the two component system AgrC/AgrA which is part of the Agr communication system. We investigated the role of AgrA for L. monocytogenes adaptation to soi!. A 6agrA mutant displayed significantly reduced survival in soilmicrocosms. Additionally, microarray analyses identified 386 genes and a large repertoire of ncRNA as differentially transcribed between the mutant and the parental strain. The results presented here suggest that AgrA may be critical for the adaptation of L. monocytogenes by regulating an important network of genes and ncRL"fAs. Moreover, co-inoculation of mutants of the Agr system with the parental strain showed that inactivation of the regulator AgrA resulted in a decrease of the fitness of the strain, confinning that A grAis necessary for optimal L. monocytogenes adaptation. On the other hand, when co-cultured with the parental strain, the fitness of the 6agrD mutant was not affected, indicating that the mutant 6agrD took advantage of the parental strain. Soi! biology is a major extrinsic factor that conditions the fate of L. monocytogenes populations in soi!. Inactivation o microbial communities lifted growth inhibition. Experimental erosion of soi! microbial diversity showed that highly diverse soi! microbial communities act as a biological barrier against L. monocytogenes invasion and that phylogenetic composition of the community also has to be considered. These results suggest that erosion of diversity may have damaging effects regarding circulation of pathogenie microorganisms in the environrnent.