How do plasmids spread antibiotic-resistance genes between bacteria?

Plasmids spread antibiotic-resistance genes primarily through a process called conjugation, which involves the direct transfer of genetic material between bacterial cells.1

Mechanisms of Spread

• Conjugation: This is the most efficient method for spreading resistance. Certain plasmids, known as conjugative plasmids, encode the machinery necessary to mediate their own transfer. In many gram-negative bacteria, the donor cell produces a specialized structure called a sex pilus, which attaches to a recipient cell. This creates a conjugal bridge, allowing the plasmid to move from the donor to the recipient.1
• Transposable Elements: Antibiotic-resistance genes are often carried on mobile genetic elements known as transposons ("jumping genes"). These elements can move into plasmids, which then act as vehicles to transport these resistance genes between different bacterial species.23
• Selective Advantage: Once a bacterium acquires a resistance plasmid, it gains a significant survival advantage in environments where antibiotics are present. This allows the resistant strain to thrive and multiply, further facilitating the spread of these genes throughout a bacterial population.423

By carrying genes that encode enzymes capable of inactivating antibiotics, these transmissible plasmids have become a major factor in the global rise of antibiotic-resistant pathogens.2