The Protection Of Subunit-vaccines Against Either S. Agalactiae Or S. Aureus Induced Mastitis In A Mouse Model

Bovine mastitis is a common disease in the worldwide dairy farms, which causes a lot of losses all over the world.S.agalactiae and S.aureus are two important human pathogens. In addition, they are also the most common etiologic agents of contagious bovine mastitis, which results in reduction in both the quantity and quality of the milk. And now, there are no effective vaccines for the bovine mastitis that caused by these two pathogens. Sip and GapC are the two highly conserved surface proteins of S. agalactiae, and C1fA is a highly conserved protein and important adhesin of S. aureus.All of the three proteins are interesting candidate vaccines for prevention of the S.agalactiae-induced or S.aureus-induced bovine mastitis.In the present study, the clinical isolated S.agalactiae and S.aureus strains were used as the templates for the amplification of Sip, GapC and a chimeric protein rSip-C1fA.Three softwares were taken to predict the epitopes of Sip and C1fA, and a chimeric protein rSip-C1fA which contains the main epitopes of Sip and C1fA was produced. The three proteins and two inactivated bacterial strains, and sterile PBS were emulsified 1:1.5 (v:v) in the oil adjuvant respectively for the immunization of the mice. And after immunizations, the mammary glands of the mice were challenged with S.agalactiae or S.aureus.After immunizations, the results indicated that:(1) both Sip and GapC induced serum IgG production significantly more effectively than killed S.agalactiae, as indicated by the different IgG titers in the sera; (2) rSip-C1fA induced serum IgG production significantly more effectively than either killed S.agalactiae or killed S.aureus, as indicated by the different IgG titers in the sera. All of the three protein immunization altered the balance of IgG1 and IgG2a and induced a significantly higher serum level of IgGl compared with IgG2a. Opsonophagocytosis assay shows that the anti-Sip sera and the anti-GapC sera could opsonize the bovine neutrophils to ingest more S.agalactiae than that of killed S.agalactiae. And the anti-rSip-C1fA sera could opsonize the bovine neutrophils to ingest more S.agalactiae or S.aureus than the killed bacteria did. Besides, histopathological examination indicated that all of the subunit-immunized mouse's mammary glands remained the intact structures with only a few polymorphonuclear leukocytes (PMN) infiltrating into the acini.All of the results indicated that Sip and GapC subunit vaccines could induce specific and significantly protective immunity against S. agalactiae. Therefore, the chimeric protein rSip-C1fA would be a promising candidate to construct novel and universal vaccines against bovine mastitis induced by either S. agalactiae or S. aureus. Moreover, the present study also provides useful information for the further development of a multi-epitope mastitis vaccine.