Acquisition of a second multi-drug resistance-encoding element by IncM1 plasmid pACM130 abolished conjugative transfer

Within the IncM plasmid family there is a lineage that has a transposon Tn1721-based multiple-resistance island inserted in the backbone gene mucB. So far, this group includes R1215, p202c, pIGT15, pARM26, and pACM1, from Europe and the USA. A new member of this group, pACM130, was isolated at the same American hospital as pACM1 and has a similar resistance island, but also carries a copy of Tn1331 that interrupts the traY gene in the conjugation operon. The conjugative phenotype of this plasmid has been abolished, though pACM130 could be mobilized by an intact traY cloned into a laboratory vector and transformed into the same donor bacterium. •pACM130 is a member of a group of IncM1 plasmids with Tn1721-based resistance islands in mucB.•A focused comparison was made of a region of the mosaic resistance island that varies among the plasmids.•Unlike related plasmids, pACM130 has acquired a copy of Tn1331 in the traY gene.•pACM130 cannot self-transfer, but can still partially prevent entry of a second IncM1 plasmid.