# Influence of biliary salts and of the ramRA locus on Salmonella Typhimurium invasion

Etienne Giraud, Sylvie Baucheron, Benoît Doublet, Isabelle Monchaux, Kunihiko Nishino, Axel Cloeckaert

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Etienne Giraud, Sylvie Baucheron, Benoît Doublet, Isabelle Monchaux, Kunihiko Nishino, et al. Influence of biliary salts and of the ramRA locus on Salmonella Typhimurium invasion. 6. Symposium on Antimicrobial Resistance in Animals and the Environment, Jun 2015, Tours, France. 154 p. hal-02739276

HAL Id: hal-02739276

https://hal.inrae.fr/hal-02739276

Submitted on 2 Jun 2020

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Influence of biliary salts and of the ramRA locus on Salmonella Typhimurium invasion

Giraud E(1)*, Baucheron S(1), Doublet B(1), Monchaux I(1), Nishino K(2), Cloeckaert A(1)

(1) Institut National de la Recherche Agronomique, Nouzilly, France

(2) Institute of Scientific and Industrial Research, Osaka, Japan

Bile represses *Salmonella Typhimurium* (ST) cell invasion, but it remains unclear which regulation pathway and particular bile components are involved. The *ramRA* global regulatory locus has been shown to regulate, in addition to multidrug efflux genes, invasion genes of the type III secretion system 1 (TTSS-1). Overexpression of *ramA*, either ectopic or due to *ramR* mutations is associated to decreased TTSS-1 genes expression, and to decreased invasion in some ST strains. As we recently showed that bile derepresses *ramA* transcription by inhibiting the binding of the RamR repressor to the *ramA* promoter, we investigated the involvement of *ramRA* in the bile-mediated repression of invasion.

We used qRT-PCR and intestinal epithelial cells invasion assays to test the effects of primary bile salts and their derivatives on invasion, at the gene expression (*ramA* and *hilA*, the master activator of TTSS-1 genes) and phenotypic levels. Dependency of these effects on *ramRA* was tested using experimental mutants of this locus.

Individual bile salts repressed *hilA* expression and cell invasion differentially, depending on their precise structure (hydroxylations, conjugation to taurine or glycine). For example, chenodeoxycholic acid-derived salts repressed invasion, whereas cholic acid-derived salts did not. Additionally, although bile increases *ramA* expression and *ramA* overexpression decreases TTSS-1 genes expression, results observed with the *ramRA* deletion mutant suggest that the *ramRA* locus has no major role in the repression of cell invasion by bile.