The Journal of Medical Microbiology, Vol 14, Issue 4 359-370, Copyright © 1981 by Society for General Microbiology
Transferable plasmid-mediated antibiotic resistance in Bacteroides
V. O. Rotimi, B. I. Duerden and S. Hafiz
Plasmid-mediated resistance to chloramphenicol (Chlr), erythromycin (Eryr),
tetracycline (Tetr) and clindamycin (Clindr) was transferred from three
clinical isolates of Bacteroides fragilis and one faecal isolate of B.
thetaiotaomicron to strains of B. fragilis, B. distasonis and Escherichia
coli, and subsequently to B. fragilis and E. coli second-and third-stage
recipients in series. Successful transfer was achieved by membrane-filter
and centrifugation techniques that provide stable cell-to-cell contact but
not by simple mixed broth culture. Chlr Eryr Tetr and Clindr Eryr were
transferred at high frequency (1.9 x 10(-3)-1.8 x 10(-4)) but Tetr was
transferred at low frequencies (1-1.6 x 10(-6)). Segregation of resistance
markers was observed with selection for Tetr when donors were Chlr Eryr
Tetr and Chlr Tetr. All transcipients were identical with the parent
recipient strains but had the resistance markers of the donor strains.
Resistance to antibiotics other than tetracycline was cured by growth with
subinhibitory concentrations of aminoacridines and ethidium bromide for 24
h; cure of solitary Tetr required longer incubation (21 days). Identical
plasmid DNA bands were demonstrated by agarose-gel electrophoresis in all
the donor and corresponding transcipient strains but plasmids were not
found in the recipient strains or in strains cured of resistance.
Plasmid-mediated transferable antiobiotic resistance in Bacteroides spp.
may compromise the treatment of infections and may provide a reservoir of
antibiotic resistance in the intestinal flora.
