Immunoglobulin G Cleaving Species in Serum-degrading Consortia of Periodontal Bacteria

Previous experiments have indicated that the enrichment of subgingival plaque in human serum led to specific consortia of micro-organisms. The present study was undertaken to identify the role which particular organisms have in these consortia in serum degradation. Firstly, isolates from consortia were tested for their ability to degrade immunoglobulin G, the major glycoprotein in serum. From the variety of species tested, only Bacteroides intermedins, Bacteroides oralis and Eubacterium nodatum were capable of IgG-cleavage and protein-core attack. Reconstitutions of consortia showed that without 'cleavers', combinations of saccharolytic specialists such as Bifidobacterium adolescentis and Streptococcus sanguis II and/or of (poly-)peptide- and amino acid-fermenting specialists such as Peptostreptococcus micros, Eubacterium brachy and Fusobacterium nucleatum were incapable of extensive growth on serum and of immunoglobulin A and G consumption. The protein cleaving organisms make glycoproteins accessible as substrates to other members of these consortia. Furthermore, these IgG-cleavers may also enhance growth of others by eliminating host-defence mechanisms in vivo. These consortia seem well adapted to their sites of isolation from various anaerobic body infections.