Immunization, serum and stool collection, and challenge schedule. To evaluate the rSEB-associated immune response in a murine model, four groups of 10 C57Bl/6 mice were tested, designated PBS, Lactococcus lactis, pCYT:rSEB, and pSEC:rSEB administered as shown in the schedule. Each group was immunized orally on days 0/1/2, and boosted on days 14/15/16 and on days 28/29/30. During the experiment, mice were bled three times, on days 14, 28 and 42. Stools were collected on days 15, 24 and 38. Animals were challenged by 7 × 108 CFU Staphylococcus aureus ATCC 14458. The animals were killed at the end of the experiment on day 48, before splenectomy.