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.