Degradation of human immunoglobulins G and M and complement factors C3 and C5 by black-pigmented Bacteroides.

Strains of Bacteroides, Capnocytophaga and Fusobacterium were examined by immunological methods for their ability to degrade the human serum proteins IgG, IgM, C3 and C5. The proteolytic activity of the strains was measured in terms of the breakdown of serum into trichloroacetic acid-soluble material. Only black-pigmented Bacteroides strains showed proteolytic activity. Strains of B. gingivalis degraded IgG, IgM, C3 and C5, strains of B. intermedius IgG and C3, strains of B. endodontalis C3 and IgG and a strain of B. loeschei degraded only IgG. These findings are discussed in relation to the pathogenicity of the black-pigmented Bacteroides.