Characterization of the gentamicin resistance transposon Tn5281 from Enterococcus faecalis and comparison to staphylococcal transposons Tn4001 and Tn4031.

In Enterococcus faecalis, the genetic determinant encoding gentamicin resistance (Gmr) on the conjugative plasmid pBEM10 previously has been shown to be on a mobile element. In the current study, this element, termed Tn5281, was shown to relocate in the absence of homologous recombination in E. faecalis UV202. On the basis of restriction endonuclease analysis and DNA-DNA hybridization studies, Tn5281 was shown to be similar, if not identical, to the Gmr transposons Tn4001 found in Australian isolates of Staphylococcus aureus and Tn4031 found in U.S. isolates of Staphylococcus epidermidis, since all three of these transposons have symmetrically located HindIII (2.5 kb apart), ClaI (slightly more than 2.5 kb apart), and HaeIII (3.9 kb apart) sites. Restriction endonuclease digestion patterns of Tn5281 generated with HincII, ScaI, and AluI were also consistent with Tn4001 and Tn4031. By using a probe specific for the external portion of the terminal inverted repeat of Tn4031, it was determined that each terminus of Tn5281 contained a 0.35-kb HaeIII fragment and a 0.7-kb HindIII-HaeIII fragment. The sizes of these fragments are identical to those found in the staphylococcal transposons, which is a further indication that inverted repeats like IS256 are present in Tn5281. A 1-kb HaeIII fragment in pBEM10 also hybridized with this probe, which indicates that Tn5281 in pBEM10 contains a double copy of the inverted repeat at one end.