Interbacterial AI-2 communication drives stage-specific genetic programs to support Salmonella colonisation in the murine gut

The cooperative response through AI-2 allows Salmonella to coordinate and regulate its community behaviours crucial for its survival and infection. In this study, we report that Salmonella Typhimurium uses AI-2 signaling to modulate the expression of chemotaxis and motility-associated genes and the formation of flagella on the bacterial cell surface. The AI-2 acts as a chemoattractant, and the cascade mediates the chemotactic response of Salmonella. Such regulations assist in the attachment and invasion of Salmonella into intestinal epithelial cells both in vitro and in a murine model. Furthermore, we determined that HilD, known to regulate motility by induction of a chemoreceptor and SPI-1 in Salmonella, along with key SPI-1 genes, is underexpressed in the absence of LuxS/AI-2 signaling, which unravels a complex regulatory network by AI-2 in Salmonella. Beyond the initial phase, this signaling facilitates survival in the presence of polymyxin B and supports intracellular survival and persistence within epithelial cells by regulating the pmrD/AB system, thereby evading the antimicrobial peptide immune response. Additionally, our findings show that Salmonella activates its LuxS/AI-2 signalling cascade within the Caco-2 epithelial cells. Complementary observation through transcriptomic profiling revealed that LuxS/AI-2 signalling governs the coordinated regulation of genes implicated in distinct phases of Salmonella pathogenesis. Lastly, using a mouse model, we show that inhibition of LuxS/AI-2 signaling in combination with antibiotics can be an alternative therapeutic approach. Thus, our study dissects an integrated regulatory mechanism by which AI-2 signaling mediates critical processes during multiple stages of Salmonella Typhimurium pathogenesis. Overall design: The STM WT and STM ?luxS, STM ?lsrK, and STM ?lsrB knockout strains were grown in vitro in LB media till mid-log phase at 37? under 170rpm shaking conditions, and then isolated RNA for sequencing