For many years, it has been considered a well known fact that the gene transfer of antibiotic resistant genes is induced in the presence of antibiotics. A study perfomed at Duke University, however, has recently disproved this mainstreamed theory with few exceptions.
A form of horizontal gene transfer called conjugation was theorized to be the cause of populations of resistant bacteria. "Because the number of resistant bacteria rises when antibiotics fail to kill them, researchers assumed that the drugs increased the amount of genetic swapping taking place." But, the study performed determined that this increase in resistant bacterial cell count was due to the parent lineages being killed by antibiotics. Thus, allowing the resistant strain to thrive.
Bacteria were suspended in G0 phase. Ten drugs, representative of each major class of antibiotic, was added to each sample. The total rate of gene exchange was tested and, for all but few exceptions, no antibiotic resistance was observed to exchange between microorganisms. To learn more about conjugation, gene transfer, and antibiotic resistance, visit this site on antimicrobial resistance.