Taxonomy of the Bacteroides: I. Deoxyribonucleic Acid Homologies Among Bacteroides fragilis and Other Saccharolytic Bacteroides Species

Abstract

Strains of the “Bacteroides fragilis group” and other saccharolytic intestinal bacteroides were delineated by deoxyribonucleic acid homology. Of the 340 strains studied, about 90% belonged to any 1 of 10 major homology groups: The named species B. fragilis, B. vulgatus, B. distasonis, B. thetaiotaomicron, B. ovatus, B. uniformis, and B. eggerthii, a described group temporarily designated “subsp. a,” and groups “3452-A” and “T4-1.” Organisms belonging to the two latter groups had phenotypic similarities with and had not been previously differentiated from B. distasonis. Thirty more strains had no homology with the above-mentioned groups and appeared to be very heterogeneous when compared among themselves. There were two subgroups within the B. fragilis homology group. These subgroups had about 65 to 70% intergroup homology and about 80 to 90% intragroup homology. The B. ovatus and B. thetaiotaomicron homology groups had similar levels of heterogeneity, but they were more complex in that they appeared to have greater numbers of subgroups. The rest of the homology groups were quite homogeneous, usually having 80 to 90% intragroup homology.