Salmonella Typhimurium Resists Calprotectin-Mediated Manganese Withholding In The Inflamed Gut Via The SitABCD and MntH High-Affinity Manganese Transporters

The pathogen Salmonella Typhimurium causes gastroenteritis and elicits a host response that reduces the availability of essential metal ions. Calprotectin, which strongly binds manganese, is a host antimicrobial protein induced in the inflamed gut. Salmonella can replicate in the inflamed gut because it acquires metals in this hostile environment. Manganese is important for Salmonella pathogenicity but the role of Mn²⁺ acquisition in the inflamed gut is unknown. We therefore hypothesized that manganese acquisition in the inflamed gut promotes Salmonella colonization. We tested whether the Salmonella transporters SitABCD and MntH acquire Mn²⁺ in the inflamed gut by mutating them and challenging mice with a 1:1 mixture of wild-type to mutant Salmonella to control for inter-host variations. Bacterial loads were determined from fecal pellets collected 48, 72 and 96 hours post-infection (p.i.) as a proxy for cecal colonization. Wild-type Salmonella outgrew the ΔsitA mutant 75:1 (96 hr p.i., P≤0.01) and the ΔmntH mutant 40:1 (48 hr p.i., P≤0.01) in the inflamed cecum. Wild-type Salmonella also outgrew the double-deletion mutant ΔsitA ΔmntH 965:1, 557:1, and 655:1 (48, 72 and 96 hr p.i. respectively, P≤0.01). In calprotectin deficient mice, the competitive advantage of wild-type Salmonella over the double-deletion mutant decreased to 60:1 only at 48hr p.i. (P≤0.05), but not at 72 and 96 hr p.i. Our data demonstrate that SitABCD and MntH synergistically promote Salmonella colonization of the inflamed cecum, compete with calprotectin for manganese sequestration early during infection, and suggest that other host factors or the microbiota may sequester manganese at later stages.