Emergence of Tn, a New Transposon in -Harboring Plasmids Associated with Increased Plasmid Stability.

OXA-48 is the most common carbapenemase in in Germany and many other European countries. Depending on the genomic location of , OXA-48-producing isolates vary in phenotype and intra- and interspecies transferability of . In most bacterial isolates, is located on one of seven variants of Tn (Tn to Tn and invTn). Here, a novel Tn variant, Tn, is described, which was identified in 11 clinical isolates from 2016 to 2020. Tn differs from Tn by the insertion of the 8,349-bp Tn family transposon Tn between the gene and open reading frame. Tn carries genes coding for a restriction endonuclease and a DNA methyltransferase as cargo, forming a type III restriction modification system. Tn was carried on an ~71-kb IncL plasmid in 9/11 isolates. In one isolate, Tn was situated on an ~76-kb plasmid, harboring an additional insertion sequence in the plasmid backbone. In one isolate, the plasmid size is only ~63 kb due to a deletion adjacent to Tn that extends into the plasmid backbone. Mean conjugation rates of the Tn-harboring plasmids in J53 ranged from 4.47 × 10 to 2.03 × 10, similar to conjugation rates of other pOXA-48-type IncL plasmids. The stability of plasmids with Tn was significantly higher than that of a Tn-harboring plasmid . This increase in stability could be related to the insertion of a restriction-modification system, which can promote postsegregational killing. The increased plasmid stability associated with Tn could contribute to the further spread of OXA-48.