Horizontal Gene Transfer
One-Sentence Definition
Horizontal gene transfer (HGT) is the movement of genetic material between organisms other than by parent-to-offspring inheritance — the main engine of rapid bacterial evolution and AMR spread.
Simple Explanation
Bacteria can swap useful DNA with neighbors (or pick it up from the environment), not only pass genes to their daughters.
Detailed Scientific Explanation
Three classical routes:
| Route | Vehicle | Note |
|---|---|---|
| Transformation | Free DNA | Competence systems |
| Transduction | Bacteriophage | Generalized / specialized |
| Conjugation | Direct cell contact | Plasmids, ICEs |
Mobile genetic elements: Plasmids, Transposons and Insertion Sequences, Integrons, Integrative Conjugative Elements, Genomic Islands. Defense systems (CRISPR-Cas in Bacteria, Restriction-Modification Systems) modulate which transfers succeed. HGT blurs species boundaries for traits like resistance and virulence.
Mechanism
Donor DNA enters a recipient → recombination or autonomous replication (plasmids) → selectable phenotype (e.g., antibiotic survival) enriches successful transfers.
Clinical Importance
- Explains sudden appearance of multidrug-resistant clones and virulence packages.
- Infection control must consider plasmid epidemiology, not only clonal spread.
Research Importance
- Core of microbial genomics and One Health AMR surveillance.
- Molecular Koch frameworks often involve transferring candidate virulence genes.
Diagnostic Relevance
- WGS and PCR panels detect resistance/virulence genes that may be mobile.
- Gene presence ≠ expression, but HGT explains unexpected resistance profiles.
AMR Relevance
Central. Most clinically critical resistance (ESBLs, carbapenemases, vanA, many mcr genes) rides on mobile elements via HGT.
Related Methods
- PCR · Whole-Genome Sequencing · conjugation assays (research)
Related MOCs
Related Papers
Learning Aids
Diagrams
Clinical Example
Example
Case: Ward outbreak: E. coli and Klebsiella from different patients share the same blaNDM carbapenemase on related plasmid Inc types.
Question: Mutation alone or HGT — and which route?
Answer: Conjugation of a Plasmid (HGT). Track plasmid epidemiology with Whole-Genome Sequencing, not only bacterial clone.
Videos
| Video | Why watch | Length |
|---|---|---|
| Genetic exchange overview | All three routes in one sitting | ~15–20 min class style |
| Conjugation / transformation / transduction | Alternate explanation pass | lecture |
Active Recall Questions
- List the three classical HGT mechanisms.
- Why can resistance spread faster than chromosomal mutation alone predicts?
- What is the difference between vertical inheritance and HGT?
Connections
- Elements: Plasmid
- Routes: Transformation · Transduction · Conjugation
- Selection: Mutation and Selection