The present invention provides a purified bacterial protein expressed during infection due to streptococci or enterococci and isolated from human sera, together with immunogenic fragments, analogs, inhibitors, antibodies and antigenic fragments specific thereto. Also provided is a DNA sequence coding for a bacterial protein or an immunogenic fragment or an analogue thereof expressed during infection due to Streptococci or Enterococci, together with homologues thereof, together with vectors, probes and inhibitors therefor. Also provided is fibronectin or an immunogenic fragment thereof or an analogue thereof or an antibody thereto or an antigen binding fragment thereof when used in a method of treatment or diagnosis of the human or animal body for infection due to Streptococci or Enterococci. Also provided are antibodies specific to HSP 90 or immunogenic fragments or analogues thereof for use in a method of diagnosis or treatment of the human or animal body of infection due to streptococci or enterococci due to any one of the group of S.oralis, S.gordonii, S.sanguis.