Persistence of plasmid-carrying tetracycline-resistant Escherichia coli in a married couple, one of whom was receiving antibiotics.

This paper describes an extension to an earlier account of the coliform flora carried by a married couple, one of whom was taking tetracycline for prolonged periods. The latter phase of this study was notable for the following: first, certain tetracycline-resistant Escherichia coli O antigen types persisted in one of the participants for several weeks after tetracycline was withdrawn; second, a course of ampicillin led to replacement of the tetracycline-resistant flora by one that was ampicillin resistant, but the end of the ampicillin course led to the reappearance of the tetracycline-resistant line, even though no tetracycline was being taken; and third, the tetracycline-sensitive O75 E. coli, which appeared toward the end of the survey, had not lost their plasmid but carried a derivative in which the tetracycline resistance gene(s) had been inactivated by the insertion of an extra piece of deoxyribonucleic acid with a molecular weight of about 1 megadalton.