A unique shuttle plasmid, pE5-2, previously constructed to mediate gene transfer from Escherichia coli to colonic Bacteroides spp. has also been transferred via conjugation from E. coli to isolates of Bacteroides gingivalis and B. intermedius. The transfer occurred at a frequency of 1.4 to 2 x 10(-7) per recipient. The presence of the plasmid in transconjugants was verified by hybridization of the total DNA of B. gingivalis recipients with sequences of the pE5-2 plasmid, as well as by standard plasmid isolation techniques.