Plasmid-Mediated Tigecycline Resistance in Bacterial Genomes

Tigecycline has become a vital last-resort antibiotic against multidrug-resistant Gram-negative and Gram-positive pathogens, yet the recent emergence of plasmid-mediated resistance threatens its clinical utility. Resistance determinants may be carried on mobile genetic elements that transfer rapidly between diverse bacterial species and ecological niches. Two principal mechanisms have been described: enzymatic inactivation of tigecycline by flavin-dependent monooxygenases (Tet(X) variants) and active efflux via Resistance-Nodulation-Division (RND) family pumps encoded on conjugative plasmids. Genomic surveillance has revealed a wide distribution of tet(X) orthologues in environmental reservoirs, food-animal production and clinical settings, while tmexCD-type efflux clusters have been identified in key pathogens such as Klebsiella pneumoniae. Comparative analyses of plasmid backbones, integrase-mediated gene capture and replicon diversity demonstrate how tigecycline resistance determinants co-evolve with other antibiotic-resistance genes, facilitating global dissemination. Understanding the molecular architecture, evolutionary history and transmission dynamics of these mobile elements is critical to inform stewardship, diagnostic development and intervention strategies under a One Health framework.

Research from Nature Portfolio

Recent studies have traced the evolutionary origins and environmental reservoirs of tet(X) genes, demonstrating that Flavobacteriaceae species harbour chromosomal monooxygenase genes with high sequence similarity to clinically observed tigecycline-inactivating enzymes. Phylogenetic and comparative-genomic analyses reveal multiple orthologues that have mobilised onto plasmids and diversified over thousands of years, underscoring the role of environmental bacteria as ancestral sources. Another investigation expanded the known repertoire of tet(X)-like genes by functional selection from metagenomic libraries of human and environmental samples. Detailed biochemical and structural characterisation of one enzyme, Tet(X7), confirmed its ability to degrade tigecycline and other tetracyclines, while the study also identified small-molecule inhibitors capable of restoring antibiotic efficacy against enzyme-expressing strains. These findings highlight both the complexity of the mobile tigecycline resistome and potential avenues for mitigation.

Plasmid-Mediated Tigecycline Resistance in Bacterial Genomes publication trend

The graph below shows the total number of articles in plasmid-mediated tigecycline resistance in bacterial genomes across all publications each year (not limited to Nature Index journals).

Technical terms

Plasmid: A self-replicating, extrachromosomal DNA molecule in bacteria that often carries antibiotic resistance genes and can be horizontally transferred between cells.

Tigecycline: A glycylcycline antibiotic used as a last-line treatment against multidrug-resistant bacterial infections.

Resistance-Nodulation-Division (RND) efflux pump: A membrane-embedded protein complex that actively exports a wide range of antibiotics out of bacterial cells, reducing intracellular drug concentration.

Tet(X) enzymes: Flavin-dependent monooxygenases that chemically inactivate tetracyclines, including tigecycline, by oxidation.

Replicon: The region of a plasmid containing the origin of replication, determining its maintenance and compatibility in bacterial hosts.

Integrase: An enzyme that mediates site-specific recombination, enabling insertion or excision of mobile genetic elements that carry resistance genes.

References

1. Emergence of a Plasmid-Encoded Resistance-Nodulation-Division Efflux Pump Conferring Resistance to Multiple Drugs, Including Tigecycline, in Klebsiella pneumoniae. mBio (2020).
2. Deciphering the Structural Diversity and Classification of the Mobile Tigecycline Resistance Gene tet(X)-Bearing Plasmidome among Bacteria. mSystems (2020).
3. TetX Is a Flavin-dependent Monooxygenase Conferring Resistance to Tetracycline Antibiotics*. Journal of Biological Chemistry (2004).
4. Tetracycline-inactivating enzymes from environmental, human commensal, and pathogenic bacteria cause broad-spectrum tetracycline resistance. Communications Biology (2020).
5. Epidemiological and phylogenetic analysis reveals Flavobacteriaceae as potential ancestral source of tigecycline resistance gene tet(X). Nature Communications (2020).
6. Co-existence of a novel plasmid-mediated efflux pump with colistin resistance gene mcr in one plasmid confers transferable multidrug resistance in Klebsiella pneumoniae. Emerging Microbes & Infections (2020).
7. Plasmid-mediated tigecycline-resistant gene tet(X4) in Escherichia coli from food-producing animals, China, 2008–2018. Emerging Microbes & Infections (2019).