A type IVB secretion system contributes to the pathogenicity of Yersinia pseudotuberculosis strains responsible for the Far East scarlet-like fever

Yersinia pseudotuberculosis is a food-borne pathogen responsible for a self-limiting gastrointestinal disease in humans known as mesenteric lymphadenitis. A phylogenetically distinct Y. pseudotuberculosis cluster from lineages 1 and 8 is associated to a specific syndrome called the Far East scarlet-like fever (FESLF), characterized by skin rash, hyperemic tongue and desquamation. Genome sequencing of FESLF strains previously revealed the presence in the plasmid pVM82 of dot/icm genes, homologous to those known to encode a T4BSS in the intracellular pathogens Legionella pneumophila and Coxiella burnetii. In the present article, we characterized the genomic features and functionality of the Y. pseudotuberculosis T4BSS (yT4BSS). We found higher dot/icm gene identity between Y. pseudotuberculosis and Pseudomonas putida genes than with those of L. pneumophila or C. burnetii. We validated the presence of all essential dot/icm genes required for the structure of a T4BSS. We then evaluated the conditions required for yT4BSS gene expression in vitro and identified an influence of temperature, with higher expression at 37{degrees}C, which mimicks the mammalian host temperature. The yT4BSS is also expressed in cellulo during the Y. pseudotuberculosis intracellular life cycle and in vivo during mouse infection. Although T4BSS functions are well characterized in the intracellular life cycle of L. pneumophila and C. burnetii, the yT4BSS appears to not be required for the intracellular survival nor for the establishment of a replication niche within cells of Y. pseudotuberculosis. Interestingly, the yT4BSS is implicated in Y. pseudotuberculosis FESLF strain pathogenicity when orally inoculated to mice but not during intravenous inoculation. Despite a role in virulence during oral infection, the yT4BSS does not influence organ colonization. However, the yT4BSS appears to be implicated in induction of important necrosis lesions in mesenteric lymph nodes and caeca of mice. Cytokine profil analyses revealed an induction of production of innate immunity related cytokines and chemokines depending on the yT4BSS in cellulo using a mouse bone marrow-derived macrophages infection model. Thus, the yT4BSS modulates cytokine responses of the host innate immune system during oral infection. In conclusion, the yT4BSS is a newly characterized virulence factor implicated in pathogenicity of Y. pseudotuberculosis strains from lineage 8 responsible for FESLF.