Horizontal gene transfer (HGT) is the exchange of genetic information between organisms, which includes the spread of antibiotic resistance genes among bacteria (except those passed down from parent to offspring), thereby, fueling pathogen evolution.Bacterial horizontal gene transfer occurs via three mechanisms: transformation, transduction, and conjugation. Conjugation is the primary mechanism for the spread of antibiotic resistance in bacteria, and it is critical in the evolution of the bacteria that degrade novel compounds such as pesticides created by humans, as well as in the evolution, maintenance, and transmission of virulence.