Transposition of a plasmid deoxyribonucleic acid sequence that mediates ampicillin resistance: identity of laboratory-constructed plasmids and clinical isolates.

The structural gene for ampicillin resistance resides upon a 3.2 X 10(6)-dalton sequence of deoxyribonucleic acid, TnA that can be transposed from replicon to replicon in laboratory experiments. TnA was transposed from a large conjugative plasmid to a small nonconjugative plasmid, RSF1010. Several RSF1010::TnA plasmids isolated in these laboratory experiments have been shown to be identical to plasmids found in clinical isolates. These data provide direct support to the theory that transposition of drug resistance genes play a key role in the evolution of R plasmids.