Wild-type strain of Staphylococcus aureus containing two genetic linkage groups for penicillinase production.

Staphylococcus aureus strain 55C1, isolated from a patient in 1955, contained two genetic linkage groups for penicillinase formation. One was linked to genes that control resistance to cadmium and mercuric ions; it had properties of a plasmidborne gene. The other was not linked to resistance to these metal ions; it had properties of a chromosomal gene. Penicillinase formation by cells that contained either linkage group was inducible by penicillins. Induced penicillinase in cells that contained both linkage groups equalled the sum of that produced in cells containing each group singly. Exopenicillinase produced by cells containing either gene was serological type A. Constitutive penicillinase formation resulting from regulator gene mutations in either linkage group was repressed to differing extents by a wild-type determinant in the trans position. The genetic structure and the regulation of penicillinase formation in strain 55C1 resembled in general those for penicillinase linkage groups which Asheshov and Dyke described for diploid mutant strains of S. aureus PS 80. There were differences in detail, however.