Horizontal Gene Transfer.

Horizontal gene transfer (HGT) is the movement of genetic information between organisms, a process that includes the spread of antibiotic resistance genes among bacteria (except for those from parent to offspring), fueling pathogen evolution. Many resistance genes evolved long ago in natural environments with no anthropogenic influence but these genes are now rapidly spreading to and among human pathogens. HGT occurs by three well-understood genetic mechanisms (Fig. 1):