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

•A multicomponent recombinant vaccine against S. aureus induced high concentrations of specific antibodies in blood and milk.•Antibodies effectively blocked the functionality of their bacterial targets in in vitro assays.•Antibodies inhibited bacterial adherence to the mammary epithelial cell line (MAC-T).•Antibodies promoted bacterial phagocytosis by bovine neutrophils. 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 60days post-calving. After calving, heifers in the VacR group produced higher total IgG (IgGtotal) titers against each component, in both serum (rBt, 3.4×105; rClf, 3.1×105; rFnBP, 2.3×105) and milk (rBt, 2.6×104; rClf, 1.3×104; rFnBP, 1.1×104), than control heifers (P