Maltose facilitates Salmonella growth under nitrogen stress while impairing adhesion to epithelial cells

The composition of nutrients in the intestine defines a niche for colonising gut pathogens. The lack of nutrients suitable for pathogens due to competition from resident intestinal microbiota or dietary preferences leads to colonisation failure by pathogens. In this study, we examined the role of the sugar maltose in Salmonella Typhimurium (STM) growth under nitrogen-deficient conditions and the pathogenicity of Salmonella in the early phases of infection in C57BL/6 mice and colon carcinoma cells (Caco-2 cells). Bacteria grown under nitrogen-deficient conditions with maltose supplementation showed enhanced growth with reduced Salmonella pathogenicity island 1 (SPI-1) expression, leading to reduced invasion of Caco-2 cells and reduced organ burden in C57BL/6 mice. Even without nitrogen starvation, maltose supplementation at lower concentrations inhibited STM colonisation in the ileum of mice. In the cell line model, deleting the maltose metabolism gene ( malQ ) leads to increased adhesion due to increased expression of type 1 fimbriae. We propose that maltose modulates Salmonella survival by aiding growth under nitrogen-deficient conditions, and it is detrimental to bacterial infection in epithelial cells.