BREAKDOWN OF VARIOUS SERUM-PROTEINS BY PERIODONTAL BACTERIA

The capacity of subgingival microorganisms to degrade various serum pr oteins was estimated. To this end, the organisms were incubated in hea t-inactivated human serum for 48 h. Porphyromonas endodontalis and Pre votella intermedia NY 365 and NY 655 completely degraded IgG, IgA and IgM. Porphyromonas gingivalis, P. asaccharolytica, Prevotella nigresce ns and P. intermedia ATCC 25611 also performed complete degradation of IgA and IgM, but partial breakdown of IgG. Cleavage of IgG by the lat ter four microorganisms, in addition to Prevotella oralis and Capnocyt ophaga ochracea, yielded Fab and Fc fragments. Degradation of various other serum proteins by P. endodontalis, P. gingivalis, P. intermedia and P. asaccharolytica included the iron-handling proteins albumin, ha ptoglobin, haemopexin and transferrin. Only P. endodontalis failed to degrade albumin. Extensive breakdown of serum proteins, in particular immunoglobulins and iron-handling proteins, will sustain bacterial gro wth and hamper local host defences. This suggests an important role fo r proteolytic microorganisms, such as Porphyromonas and Prevotella spe cies, in the causation of polymicrobial infections.