Studies on the Transmission of a Tigecycline Resistance-Mediating (A) Gene Variant from Enterobacter hormaechei via a Two-Step Recombination Process.

To investigate the contribution of a (A) variant to tigecycline resistance in Enterobacter hormaechei and the recombination events that occurred during transmission of this variant. MICs were determined by broth microdilution. G17 was characterized by PCR, transfer assay, S1-PFGE, Southern blot hybridization, and WGS analysis. A (A) variant conferring resistance to tigecycline was present in G17. This strain harbored two resistance plasmids (pG17-1, 264,084 bp and pG17-2, 68,610 bp) and its E. coli transformant T-G17 one resistance plasmid (pTm-G17, 93,013 bp). The comparative analysis of pG17-1, pG17-2, and pTm-G17 showed that a (A) variant-carrying multiresistance gene cluster (~23 kb) originating from pG17-1 had integrated into pG17-2, forming the novel plasmid pTm-G17. In a first step, this multiresistance gene cluster was excised from pG17-1 by recombination of homologous sequences, including △Tn at both termini, thereby generating an unconventional circularizable structure (UCS). In a second step, this UCS integrated into pG17-2 via recombination between homologous sequences, including IS present on both, the UCS and pG17-2, thereby giving rise to the new plasmid pTm-G17. In summary, a (A) variant conferring resistance to tigecycline was reported in . Transfer of a (A) variant-carrying multiresistance gene cluster between plasmids occurred in a two-step recombination process, in which homologous sequences, including either △Tn or IS, were involved. Tigecycline is an important last-resort broad spectrum antimicrobial agent. This study describes the two-step recombination processes resulting in the transfer of the (A) variant gene between different plasmids in , which depicts the role of recombination processes in the generation of UCSs and new plasmids, both carrying a (A) variant conferring resistance to tigecycline. Such processes enhance the dissemination of resistance genes, which is of particular relevance for resistance genes, such as the (A) variant. The presence and transmission of a (A) variant in will compromise the efficacy of tigecycline treatment for associated infection.