Antibiotics | ICECleSHZ29: A Novel Integrative and Conjugative Element Carrying the tigecycline Resistance Gene tet(X6)

This study reports the first identification of a novel integrative and conjugative element (ICE), designated ICECleSHZ29, carrying the tet(X6) gene in Chryseobacterium lecithinasegens. It systematically characterizes the genomic structure and transferability of this element, providing new insights into horizontal gene transfer mechanisms of antibiotic resistance.

 

Literature Overview
The article "ICECleSHZ29: Novel Integrative and Conjugative Element (ICE)-Carrying Tigecycline Resistance Gene tet(X6) in Chryseobacterium lecithinasegens", published in the journal Antibiotics, reviews and summarizes the discovery of a novel ICE and its carried tet(X6) gene in antibiotic-resistant pathogens, further expanding understanding of resistance gene transmission mechanisms.

Background Knowledge
Integrative and conjugative elements (ICEs) are self-transmissible genetic elements capable of site-specific integration into bacterial genomes and horizontal transfer of antibiotic resistance genes, playing significant roles in multidrug resistance dissemination. Tigecycline, a last-resort antibiotic for treating multidrug-resistant Gram-negative pathogens, has seen emergence of variant resistance genes like tet(X6), posing global public health threats. Chryseobacterium species, commonly found in natural environments, can cause severe infections in immunocompromised individuals and have been shown to harbor diverse resistance genes, suggesting their potential as reservoirs for antibiotic resistance. This study identifies ICECleSHZ29 in C. lecithinasegens, characterizing its genomic architecture, integration site, and transferability, thereby revealing novel molecular mechanisms of ICE-mediated resistance spread.

 

 

Research Methods and Experiments
The research team isolated the multidrug-resistant strain C. lecithinasegens SHZ29 from a pig farm in Shanghai, China, and determined its minimum inhibitory concentrations (MICs) for multiple antibiotics using the microbroth dilution method. Whole-genome sequencing and bioinformatics analysis were conducted to characterize the genetic context of tet(X6), followed by PCR gap-filling strategies to assemble the complete ICECleSHZ29 sequence. BLAST analysis was performed to assess homology with known ICEs. Inverse PCR was employed to detect circular intermediates of the ICE, evaluating its excision capability, while conjugation experiments were attempted to verify horizontal transferability.

Key Conclusions and Perspectives

• ICECleSHZ29 is a novel integrative and conjugative element with a full length of 74,906 bp, inserting into the 3′ end of the tRNA-Met-CAT gene in C. lecithinasegens SHZ29 and forming 17-bp direct repeats at both ends.
• The ICE contains a ~38-kb conserved backbone region and four variable regions (VR1–VR4), with VR3 harboring multiple resistance genes (tet(X6), tet(X2), erm(F), ere(D), floR, catB, sul2, ant(6)-I, and blaOXA-1327), indicating its capacity for multidrug resistance gene accumulation.
• Phylogenetic analysis classifies this ICE type into Type I (integrating into tRNA-Met-CAT) and Type II (integrating into tRNA-Glu-TTC), with integration site divergence potentially driven by integrase gene sequence variation.
• Circular intermediates detected via inverse PCR confirm excision capability, but conjugation experiments in E. coli failed to demonstrate horizontal transfer, suggesting host range restriction to Flavobacteriaceae and Weeksellaceae bacterial families.

Research Significance and Prospects
This work reveals the first identification of tet(X6) and its genetic carrier in C. lecithinasegens, demonstrating its potential for propagation in non-traditional hosts. Future studies should evaluate the ICE's transferability across diverse hosts and trace its environmental dissemination routes to inform effective antibiotic resistance control strategies.

 

 

Conclusion
This study identifies ICECleSHZ29, a novel integrative and conjugative element carrying multidrug resistance genes including tet(X6), in C. lecithinasegens. The element exhibits site-specific integration and autonomous excision capabilities but shows limited host range, as it failed to transfer to E. coli. Results highlight the role of environmental bacteria as resistance gene reservoirs and provide new molecular targets for monitoring and controlling antibiotic resistance dissemination.

 

Xi Chen, Yifei Zhang, Chunling Jiang, Beibei Li, and Lining Xia. ICECleSHZ29: Novel Integrative and Conjugative Element (ICE)-Carrying Tigecycline Resistance Gene tet(X6) in Chryseobacterium lecithinasegens. Antibiotics.