Multiple Copies of Mobile Tigecycline Resistance Efflux Pump Gene Cluster tmexC2D2.2-toprJ2 Identified in Chromosome of Aeromonas spp.

The appearance and prevalence of novel plasmid-encoded tigecycline resistance efflux pump gene clusters tmexC1D1-toprJ1 and tmexC2D2-toprJ2 in Enterobacteriaceae have raised a threat to public health. Here, another tigecycline resistance gene cluster, tmexC2D2.2-toprJ2, was identified in two Aeromonas isolates recovered from fish meat and vegetables. Cloning confirmed the expression of tmexC2D2.2-toprJ2 mediated the resistance to tigecycline and decreased susceptibility to tetracyclines and cephalosporins in both Escherichia coli and Aeromonas. In an Aeromonas veronii strain, four copies of tmexC2D2.2-toprJ2 were located on the chromosome. Further analysis revealed that tmexC2D2.2-toprJ2 has been detected in the chromosomes of A. veronii, Aeromonas hydrophila, and Aeromonas caviae with one to four copies due to the insertion of a potential integrative transferable unit. The occurrence of multiple copies of chromosomal tmexC2D2.2-toprJ2 may act as a sink for this tigecycline resistance gene cluster, which requires continuous monitoring. IMPORTANCE Tigecycline is regarded as one of the few effective drugs against multidrug-resistant bacterial infection. However, mobile tigecycline resistance efflux pump gene clusters such as tmexC1D1-toprJ1 and its variants have been identified in both animal- and human-origin Enterobacteriaceae. In this study, we first found another efflux pump gene cluster, tmexC2D2.2-toprJ2, in the Aeromonas chromosome. This gene cluster could mediate tigecycline resistance and decrease susceptibility to tetracyclines and cephalosporins in the Aeromonas host strain. Meanwhile, tmexC2D2.2-toprJ2 was detected with multiple copies in Aeromonas spp. This multidrug resistance efflux pump gene cluster with multiple copy numbers might stably exist in Aeromonas and serve as a reservoir for tmexCD2-toprJ2, facilitating its persistent presence and spread.