Evaluation of the humoral immune response to a multicomponent recombinant vaccine against S. aureus in healthy pregnant heifers

Abstract Staphylococcus aureus is a worldwide pathogen that causes mastitis in dairy herds. Shortcomings in control programs have encouraged the development of vaccines against this pathogen. This study evaluated the vaccine candidate VacR, which included recombinant S. aureus protein clumping factor A (rClf), fibronectin binding protein A (rFnBP) and hemolysin beta (rBt), formulated with a novel immune-stimulating complex. Comparisons were made between healthy pregnant heifers that received either VacR ( n  = 8; VacR group) or phosphate buffered saline (PBS) plus adjuvant (control group) SC in the supramammary lymph node area on days 45 and 15 before the expected calving date. Blood and foremilk samples were collected from 7 to 60 days post-calving. After calving, heifers in the VacR group produced higher total IgG (IgG total ) titers against each component, in both serum (rBt, 3.4 × 10 5 ; rClf, 3.1 × 10 5 ; rFnBP, 2.3 × 10 5 ) and milk (rBt, 2.6 × 10 4 ; rClf, 1.3 × 10 4 ; rFnBP, 1.1 × 10 4 ), than control heifers ( P  1 and IgG 2 in VacR group ( P  P  S. aureus rClf and rFnBP reduced bacterial adherence to fibronectin and fibrinogen by 73% and 67%, respectively ( P  S. aureus invasion of a mammary epithelial cell line (MAC-T), resulting in 15.7% of bacteria internalized ( P  P  P   0.01) in the VacR group. The results suggest that VacR is a valuable vaccine candidate against S. aureus infections, and merits further field trials and experimental challenges.