The virulence of different black‐pigmented Bacteroides strains (BPB) was studied using monoinfections in an experimental animal model. Bacterial suspensions were injected subcutaneously in the back of mice. After four days the mice were killed and the induced inflammations were examined histologically. Bacteroides gingivalis strains, which are mostly isolated from subgingival plaque associated with adult destructive periodontitis. were characterized by inducing a spreading type of inflammation, mostly resulting in a gravity abscess or a phlegmonous abscess. Strains of Bacteroides melaranogenicus subspecies intermedius, isolated from gingivitis or periodontitis, always induced a localized abscess at the site of injection. Most Bacteroides asaccharolyticus strains, which are isolated from nonoral sites, caused a localized inflammation, and Bacteroides melaninogenicus subspecies melaninogenicus strains caused only minimal inflammation.
Culture filtrates of B. gingivalis and B. asaccharolyticus are cytotoxic for Vero cells. It is shown that the cytotoxic effect is due to the butyrate concentrations present in the culture filtrates of these strains. This cytotoxic effect proved to be reversible. Strains of the B. melaninogenicus subspecies intermedius and melaninogenicus did not produce butyrate and did not show cytotoxic activity towards Vero Cells. The significance of the production of toxic concentrations of butyrate for the etiology of especially periodontal diseases is discussed.
SUMMARY. Culture filtrates of all eight strains of Bacteroides gingivalis and all five strains of B. asaccharolyticus were toxic for Vero cells. Cytotoxicity was in general greater with material from cultures of B. gingivalis than from B. asaccharolyticus but none of the culture filtrates from eight strains of B. melaninogenicus showed activity in this test. The toxic material was released during prolonged incubation and more detailed study of preparations from one strain indicated that it had a molecular weight of less than 3500 and was heat stable.
Culttire nitrates of strains of Bacteroides gingivalis and Bacteroides asaccharolyticus contain a heat stable factor which inhibits the production of extracellular matrix by chick embryo chondrocytes and which catises vacuolization of these chondrocytes. This morphological effect appeared to be reversible. Strains of the saccharolytic species Bacteroides melaninogenicus did not have these effects. The significance of this eytotojtic effect for the etiology of periodontal diseases is discussed.
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