DNA in antibiotic preparations: absence of intact resistance genes.

Fragments of erm(E2), otrA, and aph(6) shorter than 400 bp and producer strain-specific rRNA genes were amplified from various antibiotics. The amount of genetic material and the sizes of amplicons recovered from murine feces after oral administration of a beta-lactamase-encoding plasmid indicated substantial DNA degradation in the mammalian gastrointestinal tract. These observations imply that antibiotics are no major source for horizontal resistance gene transfer in clinical settings.