Thirty-three clinical isolates of Bacteroides strains with a moderate-
to-high level of resistance to 5-nitroimidazole were compared with thr
ee strains previously studied by Southern blotting of their DNA. Wheth
er plasmid borne or chromosomally determined, all genetic determinants
that are resistant to 5-nitroimidazole belong to two hybridization gr
oups.