Translocation of Carbapenemase Gene both Internal and External to Transposons Occurs via Novel Structures of Tn and Exhibits Distinct Movement Patterns.

The gene encodes a carbapenemase that hydrolyzes almost all β-lactams, including carbapenems. The rapid emergence and international spread of this gene in seriously limit clinical treatment, posing an alarming threat for public health. Transposable elements, such as Tn, a proven transposon in Europe, the United States, and elsewhere, often play a role in the dissemination of the gene. In eastern China, the gene is frequently associated with several novel structures of Tn, but their transposition ability and mechanism of movement remain unclear. Here, we experimentally demonstrate that Tn-like transposons are capable of transferring both internal and external to the Tn element from one strain to another and that distinct transposon structures exhibit different movement patterns and transposition frequencies. This process did not involve homologous recombination. Moreover, a 5-bp duplication of the target site, a characterized signature of transposition events in the Tn family, was confirmed. Tn-like transposons were found to insert preferentially into a 5-bp region that gradually exhibits a degenerated degree of AT-rich regions from both sides to the middle and that is immediately flanked by GC-rich regions. The observation in clinical isolates of diverse sequences flanking the transposons and a 5-bp duplication of the target site, as well as the prevalence of Tn-like transposons, also sustained our experimental results. This study first gives evidence about the functional role of Tn-like transposons in transferring the gene and provides new sight into the transposable element and the dissemination of antibiotic resistance in .