Conjugative Transfer of High-level Mupirocin Resistance and the Mobilization of Non-conjugative Plasmids in Staphylococcus Aureus

A 31-kb conjugative plasmid, pXU12, encoding high-level mupirocin resistance via the mupA gene, was isolated from a multiply resistant Staphylococcus aureus isolate, MB494. pXU12 was derived by a deletion of an 8.6-kb EcoRI fragment from a approximately 40-kb plasmid in the parental isolate during curing and conjugation experiments. It transferred rapidly in conjugation experiments, with transconjugants being obtained after 15 min of mating, and mobilized a 3.0-kb erythromycin resistance plasmid, pXU13, from the parental isolate at high frequencies. The cotransfer of pXU13 by pXU12 was unaffected by varying the donor-recipient ratios in the mating mixtures or the length of incubation. pXU12 also mobilized 11 other nonconjugative plasmids belonging to different incompatibility groups and cotransferred at high frequencies. The ability of pXU12 to mobilize different nonconjugative plasmids suggested that it can be used to transfer and isolate non-conjugative plasmids from resistant S. aureus strains in the laboratory, especially from strains where phage-dependent methods of transfer are not applicable.