Phage group II staphylococcal strains with chromosomal and extrachromosomal genes for exfoliative toxin production

Staphylococcal phage group 2 strain UT0007 was previously shown to contain a high-molecular-weight plasmid containing genes for exfoliative toxin (ET) and bacteriocin production. Phage group 2 strains UT0002 and UT0003 (Tox+Bac-) underwent a twofold and ninefold loss of ET activity, respectively, after growth at 44 C for 18 h. Strain UT0002 also lost total bacteriocin activity. Both strains contained (i) a 56S plasmid that was lost from those substrains showing reduced ET activity and (ii) a 21S plasmid with a gene for cadmium resistance that could be transduced into two recipient strains. Since the ET plasmid-negative substrains still made ET, it was postulated that this residual toxin was made from chromosomal genes. In characterizing the plasmid species from strains UT0002 and UT0003, the 21S but little or no 56S plasmid deoxyribonucleic acid could be isolated after centrifugation of cleared lysates from these strains on dye-buoyant density gradients. Treatment of cleared lysates from strain UT0002 with ethidium bromide, Pronase, or sodium dodecyl sulfate, but not heat at 60 C, induced conversion of the 56S closed circular ET plasmid to a 38S open circular form as determined after centrifugation on 5 to 20% neutral sucrose gradients.