Abstract
The capacity of subgingival microorgansims to degrade various serum proteins was estimated. To this end, the organisms were incubated in heat-inactivated human serum for 48 h. Porphyromonas endodontalis and Prevotella intermedia NY 365 and NY 655 completely degraded IgG, IgA and IgM. Porphyromonas gingivalis, P. asaccharo-lytica, Prevotella nigrescens and P. intermedia ATCC 25611 also performed complete degradation of IgA and IgM, but partial breakdown of IgG. Cleavage of IgG by the latter four microorganisms, in addition to Prevotella oralis and Capnocytophaga 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, haptoglobin, 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 growth and hamper local host defences. This suggests an important role for proteolytic microorganisms, such as Porphyromonas and Prevotella species, in the causation of polymicrobial infections.