Spontaneous loss of antibiotic-resistant plasmids transferred to Escherichia coli in experimental chronic bladder infection.

Abstract

We investigated whether Escherichia coli that has been transformed with antibiotic-resistant plasmids spontaneously loses the plasmids while infecting the rat bladder. A nontransmissible antibiotic-resistant plasmid was transferred to a clinically isolated strain of E. coli. A knotted thread holding the strain was implanted into the bladder of male Wistar rats. One or 4 weeks later, the total number of bacteria and that of plasmid-carrying bacteria were measured in the bladder. When plasmid-carrying E. coli alone was inoculated, most of the plasmid-carrying E. coli were replaced with plasmid-free E. coli. When plasmid-carrying and plasmid-free E. coli were simultaneously inoculated, this replacement was accelerated. These results suggest that E. coli carrying antibiotic-resistant plasmids spontaneously lose the plasmids as time passes, and thus become sensitive to antibiotics.