Localisation of the penicillinase gene in naturally occurring Staphylococcus aureus strains.

Localisation of the penicillinase gene was studied in a total of 104 inducible Staphylococcus aureus strains selected from 10,229 bacteraemia strains isolated in the years 1957-1981. The strains represented all possible combinations of the most common patterns of phage type and susceptibility to heavy metals (cadmium, arsenate and mercury) and antibiotics. The material was further supplemented with epidemically occurring strains. Localisation of the penicillinase gene was established by isolation of penicillinase-negative variants and analysis of DNA-bands on CsCl gradients and gel-electrophoresis. Fifty-five strains contained a penicillinase plasmid; 49 had a chromosomal location. The genetic location was mainly connected with phage types. All strains belonging to the 83A complex and the majority of the strains of the 52, 52A, 80, 81 complex and of phage type 95 contained a penicillinase plasmid, whereas chromosomal location was found in all strains of group II and of the 94,96 complex. In all strains but three (group III) the resistances to heavy metals were located on the penicillinase plasmid. Association between the penicillinase plasmid and genes coding for resistance to other antibiotics was found in one tetracycline resistant strain only. Three micro-constitutive strains had chromosomally located penicillinase gene, whereas one macro-constitutive strain contained a penicillinase plasmid.