Histopathological changes in the hind foot of the mouse induced by black-pigmented Bacteroides strains

The pathogenic potential of black-pigmented Bacteroides strains was studied in an animal model in which the effect on bone tissue could be determined. Bacteria suspended in agar were injected subcutaneously in the left hind paw of a mouse. After 3-5 days, B. gingivalis strain HG 66 had caused a massive infiltration with polymorphonuclear cells, destruction of the periosteum on the metatarsals and bone resorption by osteoclasts. After 7 days only a few osteoclasts remained and reactive bone formation was observed. In a comparative study with strains of several black-pigmented Bacteroides species, differences in bone resorbing potential were seen. B. gingivalis strains caused severe inflammation which resulted in bone resorption. Strains of B. asaccharolyticus, B. endodontalis, B. intermedius, B. melaninogenicus and B. loeschei caused less inflammation and less bone resorption. Killed bacteria or agar alone caused a relatively mild inflammation and no bone resorption.