Tetracycline Resistance in Escherichia coli Bearing

1. E8cherichia coli with an R-factor conferring resistance to tetracycline was induced to high-degree resistance by pre-exposure to the antibiotic. The degree of resistance was drastically lowered by subjecting the cells to osmotic shock. 2. Resistance to tetracycline was rapidly restored by incubating the shocked cells in a glucose-salts medium containing shock proteins prepared from tetracyclinesensitive and -resistant cells. Resistance was also restored by incubating the cells inacomplexmediumwithout shockprotein. 3. The initial recovery ofresistance was followed by a secondary fall in resistance when the cells were cultured in complex medium; this secondary fall was largely prevented by the addition ofa low concentration (10,ug/ml) of tetracycline to cells. The secondary fall was significantly less in shocked E. coli cells harbouring a mutant R-factor in which tetracycline resistance is largely constitutive. 4. Tetracycline resistance was also transiently depressed by treating R-factor-bearing cells with EDTA in tris buffer. 5. The significance of these results in relation to the mechanism of tetracycline resistance in R-factor-bearing cells is discussed.