Plasmid for tetracycline resistance in Staphylococcus epidermidis.

A plasmid determining tetracycline resistance was demonstrated for Staphylococcus epidermidis. Tetracycline resistance was spontaneously lost from a S. epidermidis strain at a frequency of <0.1 to 1.3%. Frequency of loss was not appreciably enhanced by growth at 42 C or in ethyl violet. The rate of transduction of tetracycline resistance in three S. epidermidis crosses was decreased as a function of ultraviolet irradiation of the transducing phage. Plasmid deoxyribonucleic acid (DNA) associated with tetracycline resistance was isolated by CsCl-ethidium bromide dye-buoyant density gradients. The tetracycline plasmids from S. aureus RN 1304 (molecular weight 2.66 Mdals) and S. epidermidis 367(phi367) (T(367)) cosedimented in 5 to 20% neutral and alkaline sucrose gradients and are therefore of similar molecular weights. An extrachromosomal element in the recipient strain, isolated as covalently closed circular DNA, did not retain its integrity in an alkaline sucrose gradient.