Vij, R.; Mukherjee, D.; Parmar, K.; Chakravortty, D.

To establish infection, Salmonella confronts a dynamic barrage of host-induced stresses. The peptidoglycan layer, essential for maintaining cell integrity and counteracting environmental stress, relies on the lipid carrier undecaprenyl phosphate, generated by Undecaprenyl pyrophosphate phosphatase (UppP). While UppP is linked to virulence in other pathogens, its role in Salmonella remains unclear. We show that an uppP mutant in S. Typhimurium exhibits altered cell morphology, reduced stiffness, and impaired survival in RAW 264.7 macrophages. The mutant is also attenuated in systemic infection in C57BL/6 mice. These defects are associated with increased sensitivity to nitrosative stress. Notably, iNOS inhibition or deficiency restores intracellular survival of the uppP mutant in both RAW 264.7 macrophages and the mouse model, implicating UppP in resistance to nitrosative stress. Our findings reveal a moonlighting role for UppP in promoting Salmonella survival within macrophages and contributing to systemic pathogenesis.