Protective effect of ligand-binding domain of fibronectin-binding protein on mastitis induced by Staphylococcus aureus in mice

The immunoprotective effect of the ligand-binding domain of fibronectin-binding protein (lFnBP) from Staphylococcus aureus (S. aureus) was investigated in a mouse mastitis model. The recombinant lFnBP (rlFnBP) and inactivated S. aureus were emulsified in Freund's adjuvant, mineral oil adjuvant or Seppic adjuvant, respectively. Seven groups of mice (n = 12 each) were immunized with these six vaccines or phosphate-buffered saline. The immunoglobulin G (IgG) titers of mice immunized with rlFnBP vaccine were higher than those in the inactivated vaccine group (P < 0.01). Antiserum capacities to opsonize adhesion and phagocytosis were significantly greater in the rlFnBP immunization group than in the killed bacteria group (P < 0.05). The immunized lactating mice were challenged with S. aureus. At 24 h postinfection, the numbers of bacteria recovered in the rlFnBP group were significantly lower than those in the killed bacteria group (P < 0.001). Levels of both interleukin-6 (IL-6) and interferon-γ (IFN-γ from the mammary glands in the rlFnBP group were higher than those in the inactivated group (P < 0.05). Better protection of mammary gland tissue was shown in the rlFnBP group. Thus, the rlFnBP, emulsified in an oil adjuvant, provided strong immune protection against S. aureus mastitis in mice, and could therefore be a promising vaccine candidate against bovine mastitis induced by S. aureus.