Penicillin and tetracycline resistance plasmids in Staphylococcus epidermidis

The genetic nature of penicillin (Pc) and tetracycline (Tc) resistance plasmids in Staphylococcus epidermidis were studied and compared with those in S. aureus. Of 10 S. epidermidis strains transduced for penicillin resistance, we could isolate Pc plasmids from only 3. One of these plasmids also encoded for cadmium resistance and another encoded for resistance to ethidium bromide, traits also associated with S. aureus Pc plasmids. Endonuclease fingerprinting of the Pc plasmids from the two species revealed extensive heterogeneity. Two S. epidermidis strains were also transduced for tetracycline resistance. Both harbored plasmids indistinguishable from S. aureus Tc plasmids as judged by endonuclease fingerprinting. These data suggest that genetic exchange between S. aureus and S. epidermidis occurs in vivo.