Horizontal gene transfer is responsible for widespread antibiotic resistance.
M. tuberculosis, the bacterium that causes tuberculosis (TB), is becoming increasingly resistant to antibiotic drugs.
In 2003, the first totally drug resistant strain of TB was discovered. As of 2012, this strain has become widespread.
Of the three types of horizontal gene transfer, bacterial conjugation has been the most effective at spreading antibiotic resistance.
Horizontal gene transfer has also been very useful in the field of genetics. Bacterial plasmids allowed the first genes to be cloned.