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. Understanding these mechanisms is essential for developing strategies to interfere with Salmonellas ability to cause disease. 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. Complimentary 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 AI-2 signaling is critical for organ colonization and virulence of Salmonella, and 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.