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.

[Optimization for ISSR-PCR system of traditional Chinese medicine Lysimachia christinae by orthogonal design].

In order to establish the stable andreliable ISSR-PCR System of Lysimachia christinae, L16 (4(5)) orthogonal design, which based on 7 levels of single factor experiment, were used in this study. The variance analysis was carried out by SPSS 19.0, and 5 main factors affecting the reaction system were optimized in 4 levels. The best annealing temperature was selected by the optimized reaction system. And the stability and reliability of this system was tested by 23 samples from different origins. The results showed that the five factors (DNA template, primer, dNTP, Mg2+ and Taq enzyme) were the most impacts on the amplified results of ISSR-PCR of L. christinae. The order of the influence was: primer > Taq enzyme > DNA template > Mg2+ > dNTP. The optimal system, which was determined by multiple comparison on different levels of each factor, was total volume of 25 microL, including DNA template 60 ng, primer 0.3 micromol x L(-1), dNTP 0.2 mmol x L(-1), Mg2+ 1.8 mmol x L(-1), Taq enzyme 1.25 U. The optimal system was stable and reliable tested by 23 samples from different origins. This study lays the foundation for genetic diversity analysis, fine varieties selection and molecular identification of L. christinae, and provides reference for optimization on ISSR-PCR system of other speciesin future.