Translocation of Carbapenemase Gene <i>bla</i> _KPC-2 both Internal and External to Transposons Occurs via Novel Structures of Tn <i>1721</i> and Exhibits Distinct Movement Patterns

Abstract

The <i>bla</i>_KPC-2 gene encodes a carbapenemase that hydrolyzes almost all β-lactams, including carbapenems. The rapid emergence and international spread of this gene in <i>Enterobacteriaceae</i> seriously limit clinical treatment, posing an alarming threat for public health. Transposable elements, such as Tn<i>4401</i>, a proven transposon in Europe, the United States, and elsewhere, often play a role in the dissemination of the <i>bla</i>_KPC-2 gene. In eastern China, the <i>bla</i>_KPC-2 gene is frequently associated with several novel structures of Tn<i>1721</i>, but their transposition ability and mechanism of movement remain unclear. Here, we experimentally demonstrate that Tn<i>1721</i>-like transposons are capable of transferring <i>bla</i>_KPC-2 both internal and external to the Tn<i>1721</i> 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<i>3</i> family, was confirmed. Tn<i>1721</i>-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<i>1721</i>-like transposons, also sustained our experimental results. This study first gives evidence about the functional role of Tn<i>1721</i>-like transposons in transferring the <i>bla</i>_KPC-2 gene and provides new sight into the transposable element and the dissemination of antibiotic resistance in <i>Enterobacteriaceae</i>.