An antigen which, as its major immunizing component, comprises a determinant of an adhesin polypeptide or an immunogenically active subsequence thereof or a precursor therefor which is convertible to an immunogenically active form, antibodies against which determinant react with the adhesin polypeptide produced by pathogenic adhesin-forming bacteria which adhere to mammalian tissue, antibodies against such antigen, and DNA expressing, as a principal gene product thereof, such antigen.