ENTEROTOXIN-BASED MUCOSAL VACCINES TO PREVENT BOVINE MASTITIS CAUSED BY STAPHYLOCOCCUS AUREUS

S. aureus represents a leading cause of bovine mastitis in dairy herds worldwide. Despite the implementation of a number of improved control practices that have helped to significantly reduce infection rates with other bacteria, S. aureus remains stubbornly problematic, due to its ability to resist common antimicrobial treatment. In addition, S. aureus is highly contagious and treatment-resistant chronic infections can spread within herds. Effective cure of animals is variable and dependent on long-term treatment, which may not be economically justified. These factors have created a need for alternative methods of prevention and elimination of this organism. Despite promising candidates, the search for an effective Staphylococcus aureus vaccine to reduce or eliminate contagious bovine mastitis caused by this organism has been disappointing, and this disease remains a high priority for the U.S. dairy industry. The protein toxin, cholera toxin (CT), secreted by the bacterium Vibrio cholerae is responsible for pathogenicity but is also a potent immunomodulator for incorporation into vaccines. CT has been developed as a mucosal adjuvant, with the ability to stimulate protective immune responses when administered via the oral, nasal or transcutaneous route. The delivery of veterinary vaccines by the mucosal route is highly desirable as a safe, effective and economical alternative to parenterally delivered vaccines. The goal of this proposal is to develop an intranasally delivered S. aureus vaccine to prevent bovine mastitis, utilizing CT and the related E.coli heat-labile toxin (LTI). We hypothesize that chimeric bacterial toxins that contain immunogenic S. aureus epitopes will elicit antigen-specific immune responses in mice and cows when delivered intranasally. Specifically, we propose to: 1) construct CT and LTI non-toxic chimeric fusions to antigens from clinical relevant strains of S. aureus, and 2) characterize the humoral immune responses against these molecules in the mouse model for the purpose of screening immunogenic chimeras and 3) characterize the humoral and functional immune responses in cows. This proposal is designed as a preliminary study to define the utility of bacterial enterotoxins for use as adjuvants in vaccines to prevent bovine mastitis. However, these studies will also provide the foundation for the rational design of experimental vaccines and mucosal adjuvants directed against a number of different infectious agents of importance to animal health.