A polypeptide, designated as "Streptococcus uberis Adhesion Molecule" (SUAM), and fragments of SUAM, prevent internalization and adherence of Streptococcus uberis and other streptococcal pathogens to cells. The SUAM polypeptide and fragments may be used diagnostically and therapeutically. Nucleic acid sequences encoding the SUAM polypeptide and fragments are included in the invention.