Plasmid analyses in clinical isolates of Bacteroides fragilis and other Bacteroides species

Abstract

Plasmid analyses were performed on Bacteroides strains isolated from clinical specimens. Of 32 Bacteroides strains, 8 contained plasmids. Of these 8 strains, 7 were B. fragilis, and the other 1 was B. distasonis. Three of these 8 strains harbored only a 3.0-megadalton plasmid. Two strains had only a 2.0-megadalton plasmid, and 1 had both a 2.0- and 3.0-megadalton plasmid. Of the remaining 2 strains, one had 2.0-, 3.0- and 5.0-megadalton plasmids, and the other had 3.0- and 5.0-megadalton plasmids. .beta.-Lactamase was produced by 93% of the clinical isolates. Seven of the 8 plasmid-carrying strains were Cd resistant, 5 were Zn resistant, 4 were Hg resistant and 2 expressed a brick-red fluorescence under UV light. None of these traits could be associated with a plasmid after performing either curing experiments or genetic transfer experiments by cell-to-cell contact.