Fusobacterium nucleatum and black-pigmented Bacteroides species adhere to red blood cells and crevicular epithelium. The attachment of the bacteroides, but not F. nucleatum, is associated with the presence of fimbriae-like structures on the bacterial surface. Such structures have been observed also in unencapsulated Bacteroides fragilis able to adhere to human red cells and cheek epithelium. Encapsulated B. fragilis adheres to porcine brush borders, but the number of adhering cells per brush border fragment is low.