A comparison was made of the amount of penicillinase produced by strains of Staphylococcus aureus carrying chromosomal penicillinase genes, plasmid penicillinase genes and strains carrying both chromosomal and plasmid genes. Plasmid genes were found to produce at least twice as much enzyme as homologous chromosomal genes. The results suggest that there are, on average, two plasmids per chromosome in exponentially growing cells.
Two inducers were used in these experiments—methicillin and 2-(2′-carboxyphenyl)-benzoyl-6-aminopenicillanicacid (CBAP). The latter proved a more efficient inducer than methicillin and this difference was most apparent when more than one i+ gene was present, which suggests that the efficiency of induction reflects the ability of the inducer to react with represser.
