High extracellular iron promotes Y enterocolitica O9 virulence, and lowering of plasma iron by minihepcidin treatment prevents mortality. (A-H) Iron-loaded HKO mice were orally infected with 10⁸ CFUs of Y enterocolitica O9 and treated with solvent or minihepcidin (Minihepc; 100 nmol). Minihepcidin treatment did not alter liver iron (A) but lowered serum iron (B) and prevented bacterial dissemination to the liver, spleen, and blood (C). (D-F) H&E or anti–Y enterocolitica antibody staining of tissue sections from the liver, spleen, and Peyer patches of solvent-treated (in red rectangles) or minihepcidin-treated (in green rectangles) HKO mice; ×10 magnification. Arrows point to bacterial abscesses. (G) Liver Saa1 mRNA expression. (H) Survival curves. (I-J) Iron-loaded HKO mice were orally infected with 10⁸ CFUs per mouse Y enterocolitica O9 and treated with solvent or minihepcidin for 7 days starting on day 2 (Minihepcidin 1) or 3 (Minihepcidin 2) after infection. (I) Survival curve. (J) Bacterial dissemination and tissue burden for minihepcidin-treated groups was assayed at euthanasia (on day 21 after infection). Tissue CFUs of iron-loaded moribund HKO mice were used for comparison (D). Survival is defined in “Methods.” Statistical analysis: The Student t test was used for normally distributed data (B; C: spleen CFUs; G) and the Mann-Whitney U test for data that were not normally distributed (A; C: liver and blood CFUs). Survival (H-I) was analyzed using Kaplan-Meier log-rank. tx, treatment.