MtlD as a therapeutic target for intestinal and systemic bacterial infections.

Unlabelled: The ability to treat infections is threatened by the rapid emergence of antibiotic resistance among pathogenic microbes. Therefore, new antimicrobials are needed. Here we evaluate mannitol-1-phosphate 5-dehydrogenase (MtlD) as a potential new drug target. In many bacteria, mannitol is transported into the cell and phosphorylated by MtlA, the EIICBA component of a phosphoenolpyruvate-dependent sugar phosphotransferase system. MtlD catalyzes the conversion of mannitol-1-phosphate (Mtl-1P) to fructose-6-phosphate, which enters the glycolytic pathway. Mutants lacking are sensitive to mannitol due to accumulation of Mtl-1P. Here, we constructed mutants in four different bacterial species (, five serovars of , and three strains of ), confirming and quantifying their mannitol sensitivity. The quantification of mannitol sensitivity was complicated by an inoculum effect and a resumption of growth following mannitol intoxication. The rate of resumption at different mannitol concentrations and cell population densities is fairly constant and reveals what is likely an intoxication processing rate. Provision of mannitol in drinking water, or by intraperitoneal injection, dramatically attenuates infection of a serovar Typhimurium mutant in mouse models of both gastroenteritis and systemic infection. Using CC003/Unc mice, we find that a mutant of serovar Typhi is also attenuated by provision of mannitol in drinking water. Therefore, we postulate that MtlD could be a valuable new therapeutic target.

Importance: The ability to treat infections is threatened by the rapid emergence of antibiotic resistance. Mannitol is a polyol used in human medicine and the food industry. During catabolism of mannitol, many bacteria transport mannitol across the inner membrane forming the toxic intermediate mannitol-1-phosphate (Mtl-1P). Mtl-1P must be processed by mannitol dehydrogenase (MtlD) or it accumulates intracellularly, causing growth attenuation. We test and confirm here that mutants of (including UPEC, and EHEC), (including serovars Typhi, and Paratyphi A, B, and C), , and experience mannitol sensitivity . Furthermore, providing mannitol in drinking water can alleviate both gastrointestinal and systemic infections in mice. This suggests that inhibition of MtlD could be a viable antimicrobial strategy.