How does horizontal gene transfer contribute to antibiotic resistance?

Horizontal gene transfer is a primary driver of antibiotic resistance in bacteria, allowing resistance traits to spread rapidly through populations. Rather than relying solely on random mutations, bacteria often acquire resistance by receiving genetic material from other cells.12

This process is largely facilitated by plasmids—extrachromosomal DNA molecules that can replicate independently. A specific class of these, known as R factors, carries genes that encode enzymes capable of altering or inactivating antibiotics, rendering them ineffective.31

These resistance genes are transmitted between bacteria through several mechanisms:

• Conjugation: The most significant method for the spread of resistance, where bacteria exchange plasmids through direct cell-to-cell contact via a conjugal bridge.42
• Transformation: The uptake of free DNA fragments from the surrounding environment.42
• Transduction: The transfer of genetic material from one bacterium to another by bacteriophages (viruses that infect bacteria).42

Once acquired, these genes may be incorporated into the recipient's genome or remain on plasmids, enabling the bacteria to survive and proliferate in the presence of antibiotics. Mobile genetic elements like transposons further accelerate this evolution by rearranging and moving these resistance genes.41