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chapitre 20; International audience; In chicken, Salmonella Enteritidis and Salmonella Typhimurium, the two main serotypes isolated in human infections, can persist in the host organism for many weeks and up to many years without causing any symptoms. This persistence generally occurs after a short systemic infection that may either lead to death of very young birds or develop into cecal asymptomatic persistence, which is often accompanied by a high level of bacterial excretion, facilitating Salmonella transmission to counterparts. Here we describe two models of chick infection. The first model reproduces well the poultry infection in farm flocks. Numerous reinfections and animal-animal recontaminations occur leading to a high level of cecal colonization and fecal excretion in all chicks in the flock, over several weeks. In the second model, these animal reinfections and recontaminations are hampered leading to heterogeneity of infection characterized by the presence of low and super-shedders. This model allows for more mechanistic studies of Salmonella/chicks interactions as animal recontaminations are lowered.

International audience; Numerous genomes are available in databases and one of the biggest challenges is to understand the function of each gene. In bacteria, transposon mutant libraries have long been used to identify genes important for bacterial survival, growth or virulence. Recent advances in high throughput sequencing now allow the screening of millions of mutants in a single or few experiments using methods such as TraDIS or Tn-seq. These methods are sensitive enough to detect small defects in mutant fitness and allow to study genes but also intergenic regions, promoter regions and essential protein domains in coding sequences if the library is saturated with transposon insertions. Here, we present the construction and the characterization of a saturated library in Salmonella Typhimurium ATCC 14028 virulent strain, which is commonly used in research laboratories. This library was obtained using the Himar1 transposon that randomly inserts into TA dinucleotides sites onto the genome. Transposon mutant library was sequenced with an Illumina NextSeq 500. After read mapping, further analyses were carried out with the TRANSIT software. These analyses confirmed saturation of the transposon mutant library both on the chromosome and the virulence plasmid. This allowed us to determine the essential genes and those providing advantage or disadvantage for bacterial growth. This Tn-seq library is now used in several research projects and is available to the scientific community through collaboration