Genetic Studies on Plasmid-Linked Cadmium Resistance in Staphylococcus aureus

Abstract

The genetic basis of cadmium resistance conferred by three penicillinase plasmids, PI 524 , PI 258 , and PII 147 , of Staphylococcus aureus was examined by mutation, recombination, and deletion analysis. Three separate loci were identified: cadA , responsible for high-level resistance; cadB , giving a low-level resistance, nonadditive to cadA ; and mad , a locus marginally decreasing the cadmium resistance of plasmid-positive staphylococci. The loci cadA and mad were present on all three plasmids, but cadB was only found on PII 147 . Spontaneous deletions of mad involved up to three-fourths of the plasmid genome, which allowed derivation of a partial deletion map of PII 147 , a plasmid with a contour length of 10.9 μm, corresponding to a molecular weight of 20.4 × 10 6 .