A conjugative transposon (Tn919) in Streptococcus sanguis.

Streptococcus sanguis FC1, originally isolated from dental plaque, was found to be naturally resistant to tetracycline. Although no plasmid DNA could be detected, tetracycline resistance was transferable in filter matings to Streptococcus faecalis FA2-2. Again, no plasmid DNA was detectable in transconjugants, and the latter could donate tetracycline resistance to S. faecalis, S. sanguis, and Streptococcus lactis. The tetracycline resistance element was able to transpose to several sites on the S. faecalis hemolysin plasmid pAD1 and in each case resulted in a 15-kilobase insert. DNA filter blot hybridization studies showed that the element bears significant homology with the conjugative transposon Tn916. Designated Tn919, it was cloned into an Escherichia coli plasmid vector (pGL101) and, as has been shown for Tn916, excised readily in the absence of selective pressure.