The staphylococcal insertion sequence IS257 is active

The plasmid pJ3356 confers high-level mupirocin resistance on a strain of Staphylococcus aureus isolated from a hospital. The plasmid also carries two copies of IS257. Recombination of an IS257-containing plasmid conferring erythromycin resistance, pOX7-IS, into either of the IS257s of pJ3356 has been observed. The co-integration of pJ3356 and a small plasmid, pOX7, is also reported and involves duplication of one of the IS257s from pJ3356 together with 8 bp of pOX7 at the site of integration. Thus IS257 has been shown to be an active mobile genetic element. (C) 1995 Academic Press, Inc.