S. Tm in cLN from ciprofloxacin-treated mice are sufficient for initiating an infection.

C57BL/6 mice were infected for 1 d with S. Tm before ciprofloxacin therapy was started (2×62 mg/kg/d by gavage). Recipient mice remained uninfected and were also treated with ciprofloxacin. (Left) 3 d p.i. mice were sacrificed and single-cell suspensions of the cLN or spleen or cecal content were transferred into antibiotic-treated naïve recipient mice. Four days later, recipient mice were sacrificed and pathogen loads in the respective organs were determined. Transfer of cLN cells leads to significantly higher infection rates compared to transferred spleen cells, cecum content, or S. Tm cultured in LB (right part; Fisher's exact test, p = 0.00482). (Middle) Relapse control. Mice were infected for 1 d with S. Tm, treated with ciprofloxacin for 2 d, and left untreated for 4 additional days. Then, we analyzed pathogen loads in the cecum content, cLN, spleen, and liver.