Identification of a conjugative R plasmid in Bacteroides ochraceus capable of transfer to Escherichia coli

Abstract

CONJUGATIVE plasmids specifying multiple antibiotic resistance are commonly found in facultative enteric bacteria. However, R plasmids have not been well characterised in anaerobic organisms, which constitute the major flora of the alimentary tract of mammals. An increasing percentage of anaerobic bacteria isolated from clinical infections are resistant to previously useful antibiotics^1,2. Several strains of Bacteroides have been reported to contain extrachromosomal DNA, but no function could be attributed to these plasmids^3–6. Recently, Mancini and Behme⁷ demonstrated transfer of antibiotic resistance from Bacteroides fragilis to an Escherichia coli recipient. However, the individual resistance markers were unstable in the E. coli transconjugants, and the presence of closed circular plasmid DNA in either the B. fragilis donor or the E. coli recipient was not demonstrated. We have previously reported the isolation of two plasmids from a strain of B. ochraceus⁵. In the present report the larger plasmid is characterised as a conjugative, multiple antibiotic resistance factor. In addition, it is shown that both plasmids can be transferred to and stably maintained in E. coli.