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

This study is the first to identify a novel integrative and conjugative element (ICECleSHZ29) carrying the tet(X6) gene in Chryseobacterium lecithinasegens, revealing its genomic structure and transfer capability. These findings provide new insights into horizontal transfer mechanisms of antibiotic resistance genes.

 

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 the discovery of novel ICEs harboring tet(X6) in drug-resistant pathogens. This expands current understanding of resistance gene dissemination mechanisms.

Background Knowledge
Integrative and conjugative elements (ICEs) are self-transmissible mobile genetic elements capable of site-specific integration into bacterial genomes, playing significant roles in spreading multidrug resistance. Tigecycline, a last-line antibiotic against multidrug-resistant Gram-negative pathogens, faces emerging resistance due to tet(X) family gene variants like tet(X6), posing global public health threats. Chryseobacterium species, widely distributed in natural environments, can cause severe infections in immunocompromised individuals and have been recognized as reservoirs for diverse resistance genes. This study reports the first identification of a tet(X6)-carrying ICE in C. lecithinasegens, designated ICECleSHZ29, with systematic analysis of its genetic architecture, integration site, and transferability, offering novel molecular insights into ICE-mediated resistance gene propagation.

 

 

Research Methods and Experiments
The research team isolated the multidrug-resistant strain C. lecithinasegens SHZ29 from a pig farm in Shanghai, China. Minimum inhibitory concentrations (MICs) against various antibiotics were determined using the microbroth dilution method. Whole-genome sequencing combined with bioinformatics analysis characterized the genetic environment of tet(X6). The complete ICECleSHZ29 sequence was assembled through PCR gap-filling strategies, with homology analysis conducted via BLAST. Circular intermediates of ICECleSHZ29 were detected by inverse PCR to assess excision capability, and conjugation experiments were performed to evaluate horizontal transfer potential.

Key Conclusions and Perspectives

• ICECleSHZ29 represents a novel integrative and conjugative element with a full length of 74,906 bp. It inserts into the 3′ end of the tRNA-Met-CAT gene in C. lecithinasegens SHZ29, forming 17-bp direct repeats at both integration junctions.
• The element contains a ~38 kb conserved core backbone and four variable regions (VR1–VR4). VR3 harbors multiple resistance genes including tet(X6), tet(X2), erm(F), ere(D), floR, catB, sul2, ant(6)-I, and blaOXA-1327, demonstrating its capacity to accumulate multidrug resistance determinants.
• Phylogenetic analysis classifies this ICE type into Type I (integrating at tRNA-Met-CAT) and Type II (integrating at tRNA-Glu-TTC), with integration site differences potentially attributed to integrase sequence variations.
• Inverse PCR confirmed circular intermediates of ICECleSHZ29, indicating excision capability. However, conjugation experiments failed to demonstrate horizontal transfer in E. coli, suggesting host range limitations within Flavobacteriaceae and Weeksellaceae families.

Research Significance and Prospects
This work reports the first identification of tet(X6) resistance gene and its mobile carrier in C. lecithinasegens, highlighting the species' potential in resistance gene dissemination. Future studies should comprehensively assess the ICE's transferability across diverse hosts and map its environmental spread pathways to develop effective resistance control strategies.

 

 

Conclusion
This study characterizes ICECleSHZ29 as a novel integrative and conjugative element carrying multidrug resistance genes including tet(X6), newly identified in C. lecithinasegens. The element demonstrates site-specific integration and autonomous excision capabilities but shows restricted horizontal transferability to E. coli, suggesting host specificity within Flavobacteriaceae and Weeksellaceae bacterial families. The findings underscore environmental bacteria's role in resistance gene propagation and provide new molecular targets for resistance monitoring and control measures.

 

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.