Genetic diversity and characteristics of high-level tigecycline resistance Tet(X) in Acinetobacter species

Chong Chen, Chao Yue Cui, Jun Jun Yu, Qian He, Xiao Ting Wu, Yu Zhang He, Ze Hua Cui, Cang Li, Qiu Lin Jia, Xiang Guang Shen, Ruan Yang Sun, Xi Ran Wang, Min Ge Wang, Tian Tang, Yan Zhang, Xiao Ping Liao, Barry N. Kreiswirth, Shi Dan Zhou, Bin Huang, Hong DuJian Sun, Liang Chen, Ya Hong Liu

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Background: The recent emergence and dissemination of high-level mobile tigecycline resistance Tet(X) challenge the clinical effectiveness of tigecycline, one of the last-resort therapeutic options for complicated infections caused by multidrug-resistant Gram-negative and Gram-positive pathogens. Although tet(X) has been found in various bacterial species, less is known about phylogeographic distribution and phenotypic variance of different genetic variants. Methods: Herein, we conducted a multiregional whole-genome sequencing study of tet(X)-positive Acinetobacter isolates from human, animal, and their surrounding environmental sources in China. The molecular and enzymatic features of tet(X) variants were characterized by clonal expression, microbial degradation, reverse transcription, and gene transfer experiments, while the tet(X) genetic diversity and molecular evolution were explored by comparative genomic and Bayesian evolutionary analyses. Results: We identified 193 tet(X)-positive isolates from 3846 samples, with the prevalence ranging from 2.3 to 25.3% in nine provinces in China. The tet(X) was broadly distributed in 12 Acinetobacter species, including six novel species firstly described here. Besides tet(X3) (n = 188) and tet(X4) (n = 5), two tet(X5) variants, tet(X5.2) (n = 36) and tet(X5.3) (n = 4), were also found together with tet(X3) or tet(X4) but without additive effects on tetracyclines. These tet(X)-positive Acinetobacter spp. isolates exhibited 100% resistance rates to tigecycline and tetracycline, as well as high minimum inhibitory concentrations to eravacycline (2–8 μg/mL) and omadacycline (8–16 μg/mL). Genetic analysis revealed that different tet(X) variants shared an analogous ISCR2-mediated transposon structure. The molecular evolutionary analysis indicated that Tet(X) variants likely shared the same common ancestor with the chromosomal monooxygenases that are found in environmental Flavobacteriaceae bacteria, but sequence divergence suggested separation ~ 9900 years ago (7887 BC), presumably associated with the mobilization of tet(X)-like genes through horizontal transfer. Conclusions: Four tet(X) variants were identified in this study, and they were widely distributed in multiple Acinetobacter spp. strains from various ecological niches across China. Our research also highlighted the crucial role of ISCR2 in mobilizing tet(X)-like genes between different Acinetobacter species and explored the evolutionary history of Tet(X)-like monooxygenases. Further studies are needed to evaluate the clinical impact of these mobile tigecycline resistance genes.

Original languageEnglish (US)
Article number111
JournalGenome Medicine
Issue number1
StatePublished - Dec 2020
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Molecular Medicine
  • Molecular Biology
  • Genetics
  • Genetics(clinical)


  • Acinetobacter species
  • Ecological niches
  • Flavobacteriaceae bacteria
  • ISCR2
  • Tigecycline resistance
  • bla
  • tet(X)


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