Abstract
Plasmids R26 (Inc P) and R55-1 (Inc C) specify inducible nonenzymatic resistance to chloramphenicol. Escherichia coli K-12 strains harboring these plasmids encoded low-level resistance to thiamphenicol analogs Sch 25298 and Sch 25393 but failed to specify resistance to the fluorinated chloramphenicol analog Sch 24893. The analogs were efficient inducers of high-level chloramphenicol resistance.