Properties of an unusual genetic element in Staphylococcus aureus.

A strain of Staphylococcus aureus (M7) contains a transmissible element determining production of penicillinase, and resistance to cadmium ions, neomycin, streptomycin and kanamycin (CPNS). This element was transferred either in toto or in fragments at low frequency from strain M7. The fragment (NS) possesses features typical of chromosomal genes and the fragment (CP), like (CPNS) itself, exhibits plasmid features. The element (CPNS) is transferred in mixed culture at high frequency, up to 10(-3), between other strains of staphylococci. Lysogenisation of the recipient increases the frequency of transfer. The frequency of transduction of (CPNS), (CP) and (NS) from cell-free lysates corresponds well with the transfer frequency of each of these elements in mixed culture. A possible mechanism for the evolution of (CPNS) is discussed.