Chromosomal integration of the novel plasmid pUR3912 from methicillin-susceptible Staphylococcus aureus ST398 of human origin

The novel erm(T)-cadDX-carrying plasmid pUR3912 has recently been described in the methicillin-susceptible Staphylococcus aureus ST398-t571 strain C3912 from a healthy human in Spain. Structural analysis revealed that pUR3912 belongs to the pC194 replicon family, replicates via a rolling circle mechanism and harbours putative double-strand (dso) and single-strand (sso) origins of replication. Besides its plasmid location, a copy of pUR3912 was also found in the chromosomal DNA of strain C3912. Two IS431 copies, which flank the plasmid, most probably mediated its chromosomal integration. Its ability to not only exist extrachromosomally, but also to integrate into the chromosomal DNA ensures persistence and dissemination of pUR3912.