Learning Objective
At the end of this section, the learner should be able to explain how plasmids and transposons contribute to antimicrobial resistance, including the structure of R-factors and common enzymatic mechanisms.
Plasmid-mediated resistance occurs when resistance genes are located on plasmids—mobile, extrachromosomal DNA elements that can move between bacteria.
Key Features
- Resistance genes often encode enzymes that chemically modify or inactivate antibiotics.
- These resistance plasmids are known as R factors.
- Tra/oriT region: Enables conjugation (transfer between bacteria).
- R-determinant region: Contains multiple resistance genes, often inserted through transposons or integrons.
Transposons (jumping genes)
Transposons are mobile DNA pieces responsible for creating multidrug resistance plasmids.
They:
- Move themselves (or a copy) between DNA molecules.
- They are found in bacteria, eukaryotes, and viruses.
- Carry at least one transposase gene.
- It can disrupt other genes when it inserts, causing mutations.
Common Plasmid-Mediated Resistance Mechanisms
| Drug Class | Mechanism |
|---|---|
| Penicillins & cephalosporins | β-lactamase cleavage of the β-lactam ring |
| Aminoglycosides | Drug inactivation by acetylation, adenylylation, or phosphorylation |
| Chloramphenicol | Acetyltransferase inactivation |
| Tetracyclines | Increased efflux pumps |
| Sulfonamides | Efflux + reduced enzyme affinity |
| Vancomycin | Modified D-Ala-D-Lac cell wall peptides preventing drug binding |
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