The present invention provides an antigenic composition, the composition comprising at least one recombinant protein. The recombinant protein comprises at least one epitope. The epitope is reactive with an antibody which is reactive with a polypeptide having the sequence set out in SEQ. ID. NO. 3 or SEQ. ID. NO. 5. The invention also provides methods and compositions for the production of the recombinant protein. Also provided are methods for the diagnosis, treatment and prevention of P. gingivalis infection.