The nature of the genetic determinant for the SHV-1 beta-lactamase.

In two unrelated plasmids of incompatibility groups FII and N the gene for the SHV-1 beta-lactamase exists as part of a transposable element of molecular weight 9.5 megadaltons. This transposon has moved onto plasmids of at least three incompatibility groups; PI, Ialpha and J. This confirms the suggestion that the recent spread of the SHV-1 beta-lactamase has been associated with the transposition of the genetic determinant of this enzyme between unrelated plasmids.