Resistance to cadmium, arsenate and mercury among Danish strains of Staphylococcus aureus isolated from cases of bacteriaemia, 1957-74.

A collection of 3040 epidemiologically-unrelated strains of Staphylococcus aureus isolated from blood cultures during the period 1957-74 was examined for their resistance to cadmium (Cd), arsenate (As) and mercury (Hg); 98% of the strains had metal-resistance patterns of (a) sensitive to all these metals, (b) resistant to Cd, (c) resistant to Cd,As or (d) resistant to Cd,As,Hg. The percentage of Cd,As,Hg-resistant strains fell from 50 to 13 in the period of investigation and the percentage of Cd-resistant strains increased from 11 to 32. Strains resistant only to Cd were mainly P resistant only and a correlation was found between multiple antibiotic resistance and Cd,As,Hg resistance. Strains of phage types 80/81, 52/52A/80/81 and 52/52A/80 were never Cd resistant only, but mainly Cd,As,Hg resistant. Strains of the 94, 96 complex were mainly Cd resistant and were never resistant to Cd,As,Hg.