How does bacterial conjugation transfer antibiotic-resistance plasmids?

Bacterial conjugation is a primary mechanism for the horizontal transfer of antibiotic-resistance genes, allowing bacteria to rapidly acquire new survival traits. This process involves the direct transfer of plasmids—small, extrachromosomal DNA molecules—from a donor cell to a recipient cell through physical contact.12

The mechanism typically proceeds as follows:

• Cell Recognition and Attachment: In many gram-negative bacteria, the donor cell produces a specialized, plasmid-encoded appendage known as a sex pilus. This structure facilitates the recognition of and attachment to a recipient cell.23
• Formation of a Conjugal Bridge: Once the donor and recipient cells are connected, they are drawn into direct physical contact, and a conjugal bridge is established between them.2
• DNA Transfer: The conjugative plasmid initiates its own transfer by moving through this bridge from the donor to the recipient. Because these plasmids often carry genes encoding enzymes that inactivate antibiotics (such as beta-lactamase), the recipient cell gains the ability to survive exposure to those specific drugs.241

This process is highly efficient and can occur between different bacterial species, contributing significantly to the widespread and rapid development of antibiotic resistance in clinical and environmental settings.21