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Tet(X4)-producing Escherichia coli isolates in Taiwan
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DOI：10.1016/j.jgar.2026.01.014.png)
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Abstract
En 中文
Objectives: Plasmid-mediaed tet(X4) , linked to high-level tigecycline resistance, was first identified in China with Escherichia coli ( E. coli ) as a major reservoir. No confirmed cases had been reported in Taiwan. Methods: We examined 81 tigecycline-resistant E. coli isolates (MIC >= 4 mg/L) collected in Taiwan from 2015 to 2022, including 71.6% carbapenem-resistant and 28.4% carbapenem-susceptible strains. Thirty-six underwent whole-genome sequencing to investigate resistance mechanisms. Results: Two isolates (2.5%) carried tet(X4) on novel plasmids (pEC1360-1 and pEC1638-1). Both plasmids contained the ISVsa3-estT- tet(X4) -ISVsa3 (IETI) element, a mobile unit capable of transposon-mediated transfer without a fixed integration hotspot. The tet(X4) -positive strains showed distinct evolutionary divergence from the first reported Chinese strain (LHM10-1). Tet(X4) was located on different Inc-type plasmids, including a 66.8 kb IncR and a 159.3 kb IncR/IncFIB(K)/IncFIA(HI1) plasmid, across various sequence types. No tet(X4) was detected in carbapenem-resistant isolates. Other resistance genes, such as cmlA1 and floR , were more prevalent in carbapenem-susceptible isolates (66.7% vs. 25.9%, P = 0.077). Conclusion: This study reports the first tet(X4) -positive E. coli isolates in Taiwan, both from carbapenemsusceptible strains. The presence of novel mobile plasmids underscores the potential for horizontal gene transfer. Continuous surveillance of tet(X) and other last-line antibiotic resistance mechanisms is essential to mitigate the risk of further spread. (c) 2026 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )
Keywords:
Tigecycline
Tigecycline-resistant E. coli
Tet (X4)
Plasmid
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