Staphylococcal penicillinase plasmids: studies on the reversion of a temperature-sensitive replication mutant to temperature stability.

A culture of Staphylococcus aureus harbouring a temperature-sensitive plasmid carrying genes for resistance to penicillin and cadmium ions, loses this plasmid and the associated phenotype when grown at the restrictive temperature. However, incubation at the restrictive temperature in the presence of cadmium ions results in a small number of cadmium-resistant cells. The properties of these surviving cells have been investigated and evidence is presented in support of the hypothesis that at least some of these cadmium-resistant cells are the result of integration of the plasmid into some other replicon, possibly the chromosome.