How does bacterial conjugation transfer antibiotic resistance?

Bacterial conjugation is a primary mechanism for the spread of antibiotic resistance, occurring through direct cell-to-cell contact. This process is mediated by plasmids—extrachromosomal DNA molecules that can replicate independently of the bacterial chromosome.123

During conjugation, a donor cell containing a conjugative plasmid produces a pilus (specifically a sex pilus in gram-negative bacteria) that attaches to a recipient cell. Once the cells are brought into direct contact, a conjugal bridge forms, allowing the plasmid to be transferred from the donor to the recipient.12

These plasmids often carry genes that encode enzymes capable of inactivating specific antibiotics, such as beta-lactamase, which renders penicillin inactive. Because these plasmids can be transferred between different bacterial species, resistance can spread rapidly through a population. While antibiotics do not create these resistant strains, they exert selective pressure that allows the newly resistant bacteria to survive and replicate while sensitive organisms are eliminated.421