Effect of the prophage and penicillinase plasmid of the recipient strain upon the transduction and the stability of methicillin resistance in Staphylococcus aureus.

Transduction of a methicillin-resistance determinant (mec) in Staphylococcus aureus RN450 was dependent on its prior lysogenization with an appropriate temperate phage. In addition, an appropriate transduced penicillinase plasmid was usually required. Some phage 80-resistant variants of RN450 or of its parental lysogenic strain, NCTC 8325, were also effective recipients for transduction of mec. Elimination of prophage from RN450 abrogated its effectiveness as a transductional recipient of mec. Elimination of prophage from a methicillin-resistant transductant of RN450 reduced resistance to undetectable levels in six of seven phage-eliminated strains. In four of these a variable number of clones again became phenotypically resistant after lysogenization alone or lysogenization combined with reintroduction of a penicillinase plasmid. In two prophage-eliminated strains, no evidence of residual mec could be adduced. The establishment, expression, or stability of the transduced mec in strain RN450 appeared to depend on some function determined by a prophage or a prophage and a penicillinase plasmid.