Nature of the Determinant of Tetracycline Resistance in Staphylococcus Aureus

Ninety-one tetracycline-sensitive mutants were isolated from naturally occurring tetracycline-resistant strains of Staphylococcus aureus. Only two mutants reverted to the typical wild type. All of the sensitive mutants tested were competent recipients of the tetracycline marker. In 150 crosses between non-reverting mutants, no tetracycline-resistant recombinants were observed. Transduction frequencies obtained with ultraviolet irradiated phage lysates indicated that the tetracycline determinant is an extrachromosomal gene resistant to the low dose of ultraviolet used. The penicillinase determinant may be either on the chromosome or in the cytoplasm, depending on the strain tested.