IS26-Flanked Composite Transposon Tn6539 Carrying the (M) Gene in IncHI2-Type Conjugative Plasmids From Isolated From Ducks in China.

Tet(M)-type proteins confer resistance to tetracycline and related antibiotics by interacting with the ribosome. Genes encoding Tet(M) have been found in a range of bacteria, including . In the current study, conjugation experiments were performed between seven different tetracycline-resistant, azide-susceptible strains isolated from ducks and tetracycline-sensitive, azide-resistant J53. Transconjugants were obtained from two of the strains at a frequency of 1.2 × 10. PCR, southern blotting and sequencing demonstrated that (M) in the transconjugants was located on a ~50 kb IncHI2-type plasmid and was part of a composite transposon, designated Tn6539. This transposon is flanked by two IS26 elements in opposite orientation and contains the Tn3Δ+Δ--(M)+gamma delta++Δ sequences. The Δ--(M) sequence was a highly conserved genetic fragment in harboring (M) and mainly located in the composite transposons flanked by IS6-family elements. In summary, Tn6539 is a new composite transposon capable of horizontal transfer of (M) among isolates.