INTRAMAMMARY IMMUNIZATION WITH LIVE-ATTENUATED STAPHYLOCOCCUS-AUREUS - MICROBIOLOGICAL AND IMMUNOLOGICAL STUDIES IN A MOUSE MASTITIS MODEL

Mammary infection was induced in lactating mice by intramammary inject ion of Staphylococcus aureus. Histopathological analysis revealed infi ltration and lesions of varying magnitude that were still apparent 21 days after the challenge. Concomitantly, viable S. aureus was recovere d from infected mammary glands. Mice were immunized by the intramammar y route with 5 X 10(6) colony forming units of a temperature-sensitive mutant of S. aureus and subsequently received a boosting injection se ven days later. On day 14 mice were challenged by the intramammary rou te with the wild-type strain. Intramammary immunization induced a sign ificant increase in milk IgA (P < 0.05), serum IgG (P < 0.05) and seru m IgA (P < 0.05) on the day of the challenge, when compared with non-i mmunized mice. Immunization decreased significantly (P < 0.01) the num ber of S. aureus colony forming units recovered 96 h after intramammar y challenge. In conclusion, the feasibility of immunizing locally with temperature-sensitive S. aureus to induce immunity in the mouse mamma ry gland was demonstrated. The mouse model of mastitis is proposed as a useful system for screening temperature-sensitive S. aureus strains to be utilized in the development of a vaccine.