Y. pseudotuberculosis strains 32777 and 32777 ΔyopM were revived from freezer stocks on MacConkey agar. Individual colonies were cultured overnight in 2× YT at 25 °C with shaking. Mice were fasted for at least 12 h prior to gavage with 1 × 107 colony forming units in 200 μL phosphate buffered saline (PBS).