Penicillinase Production And Metal-Ion Resistance In Staphylococcus AureusCultures Isolated From Hospital Patients

Ninety-six penicillinase-producing strains of Staphylococcus aureus, all members of the phage-groups I and III, were examined for sensitivity to mercury, cadmium and arsenate.

Strains resistant to mercury, arsenate and cadmium were nearly always multiple-antibiotic resistant and produced large amounts of A-type penicillinase, much of it extracellular. They included representatives of a few widespread types of “hospital” staphylococci.

Other strains, that were sensitive to mercury but resistant to arsenate and cadmium appeared, though less frequently, to occur endemically in hospitals; they were generally sensitive to antibiotics other than penicillin and although they produced variable amounts of penicillinase, much of it was extracellular. Their penicillinase was either of the A-type or the C-type; in strains with A-type penicillinase the determinants for resistance to arsenate and cadmium appeared to be located on the penicillinase plasmid, but in strains with C-type penicillinase they appeared to be chromosomal. Penicillin-negative variants appeared relatively frequently in all but one of the cultures, suggesting that the genetic determinant for penicillinase production was on a plasmid; in one culture, however, there was evidence that it was chromosomal. Resistance to other antibiotics was not genetically linked with penicillinase production.