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Abstract In order to survive and replicate, Salmonella has evolved mechanisms to gain access to intestinal epithelial cells of the crypt. However, the impact of Salmonella Typhimurium on stem cells and progenitors, which are responsible for the ability of the intestinal epithelium to renew and protect itself, remains unclear. Given that intestinal organoids growth is sustained by stem cells and progenitors activity, we have used this model to document the effects of Salmonella Typhimurium infection on epithelial proliferation and differentiation, and compared it to an in vivo model of Salmonella infection in mice. Among gut segments, the caecum was preferentially targeted by Salmonella. Analysis of infected crypts and organoids demonstrated increased length and size, respectively. mRNA transcription profiles of infected crypts and organoids pointed to upregulated EGFR-dependent signals, associated with a decrease in secretory cell lineage differentiation. To conclude, we show that organoids are suited to mimic the impact of Salmonella on stem cells and progenitors cells, carrying a great potential to drastically reduce the use of animals for scientific studies on that topic. In both models, the EGFR pathway, crucial to stem cells and progenitors proliferation and differentiation, is dysregulated by Salmonella, suggesting that repeated infections might have consequences on crypt integrity and further oncogenesis.

Abstract Numerous studies have demonstrated the key role of the Salmonella Pathogenicity Island 1-encoded type III secretion system (T3SS1) apparatus as well as its associated effectors in the invasion and intracellular fate of Salmonella in the host cell. Several T3SS1 effectors work together to control cytoskeleton networks and induce massive membrane ruffles, allowing pathogen internalization. Salmonella resides in a vacuole whose maturation requires that the activity of T3SS1 subverts early stages of cell signaling. Recently, we identified five cell lines in which Salmonella Typhimurium enters without using its three known invasion factors: T3SS1, Rck and PagN. The present study investigated the intracellular fate of Salmonella Typhimurium in one of these models, the murine hepatocyte cell line AML12. We demonstrated that both wild-type Salmonella and T3SS1-invalidated Salmonella followed a common pathway leading to the formation of a Salmonella containing vacuole (SCV) without classical recruitment of Rho-GTPases. Maturation of the SCV continued through an acidified phase that led to Salmonella multiplication as well as the formation of a tubular network resembling Salmonella induced filaments (SIF). The fact that in the murine AML12 hepatocyte, the T3SS1 mutant induced an intracellular fate resembling to the wild-type strain highlights the fact that Salmonella Typhimurium invasion and intracellular survival can be completely independent of T3SS1.