R-factor-mediated resistance to tetracycline in Escherichia coli K12: An R-factor with a mutation to temperature-sensitive tetracycline resistance

R-factor-mediated resistance to tetracycline was studied in $\text{Escherichia coli}$ K12 carrying an $\text{fi}{}^{\mathrm{+}}$ F-like R-factor which has a mutation resulting in temperature-sensitive resistance to the drug. The rate of uptake of tetracycline in this mutant is sensitive to temperature, but the rate of efflux is not. These results are consistent with the view that resistance to tetracycline is expressed at the level of the influx rather than of the efflux of tetracycline.