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Streptococcus uberis is an important environmental mastitis pathogen that causes subclinical and clinical mastitis in lactating and nonlactating cows and heifers throughout the world. Previous work from our laboratory suggests that S. uberis adhesion molecule (SUAM) is involved in S. uberis pathogenesis and may be an excellent target for vaccine development. The objective of this study was to evaluate the antibody response of cattle vaccinated with recombinant SUAM (rSUAM). Uninfected primiparous dairy cows (n = 30) in late lactation were divided randomly into three groups of 10 cows each: control, 200 mu g rSUAM, and 400 mu g rSUAM. Cows in groups vaccinated with 200 mu g and 400 mu g rSUAM received an emulsion containing adjuvant, phosphate-buffered saline (PBS) and affinity purified rSUAM. Cows in the control group received an emulsion containing adjuvant and PBS. Cows were vaccinated subcutaneously in the neck region at drying off (D-0), 28 d after drying off (D+28) and within 7 d after calving. Serum was collected at D-0, D+28, at calving (C-0), calving vaccination (CV), and during early lactation (CV+14). Serum antibody responses were measured by an ELISA against rSUAM. Following the first vaccination a significant increase in anti-rSUAM antibodies was detected at D+28 in cows from groups vaccinated with 200 mu g and 400 mu g rSUAM when compared to the control group. This increase in anti-rSUAM antibodies continued following the second immunization at D+28; reaching the highest levels in the post-parturient sampling period (CO), after which antibodies appeared to plateau. S. uberis UT888 pretreated with several dilutions of heat-inactivated serum from cows vaccinated with rSUAM, affinity purified antibodies against rSUAM, and to a 17 amino acid long peptide from the N terminus of SUAM (pep-SUAM) were co-cultured with bovine mammary epithelial cells and adherence to and internalization of S. uberis into epithelial cells was measured. Compared to untreated controls, opsonization of two strains of S. uberis with sera from cows vaccinated with rSUAM, with affinity purified rSUAM antibodies, or with affinity purified pep-SUAM antibodies significantly reduced adherence to and internalization of this pathogen into bovine mammary epithelial cells. In conclusion, subcutaneous vaccination of dairy cows with rSUAM during physiological transitions of the mammary gland either from or to a state of active milk synthesis induced antibodies in serum and milk and these antibodies reduced adherence to and internalization of S. uberis into mammary epithelial cells under in vitro conditions. SUAM appears to be an excellent candidate for vaccine development. (C) 2011 Published by Elsevier B.V.