Intramammary immunization with live-attenuated Staphylococcus aureus protects mice from experimental mastitis

Female mice were immunized by the intramammary route with live-attenuated Staphylococcus aureus according to different schedules and challenged with virulent S. aureus. Immunization in late pregnancy or early lactation induced a significant decrease (P<0.05) in the number of S. aureus CFU recovered from glands after the challenge and a significant increase (P<0.05) in the levels of milk and serum specific IgG and IgA antibodies. Mice immunized before pregnancy were not protected from S. aureus challenge. Immunization did not increase the number of somatic cells in milk when compared with control mice. Protection from S. aureus intramammary infection may be achieved if mice are locally immunized during late pregnancy or early lactation.