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

• Main Authors: Ya-wei Sun, Ying-ying Liu, Hua Wu, Ling-fei Wang, Jian-hua Liu, Li Yuan, Yu-shan Pan, Dan-dan He, Gong-zheng Hu
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2019-01-01
• Series: Frontiers in Microbiology
• Subjects: composite transposonTn6539; tet(M) gene; IS26 element; IncHI2-type plasmid; Escherichia coli isolates
• Online Access: https://www.frontiersin.org/article/10.3389/fmicb.2018.03168/full

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 Escherichia coli. In the current study, conjugation experiments were performed between seven different tetracycline-resistant, azide-susceptible E. coli strains isolated from ducks and tetracycline-sensitive, azide-resistant E.coli J53. Transconjugants were obtained from two of the strains at a frequency of 1.2 × 10−8. PCR, southern blotting and sequencing demonstrated that tet(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 Tn3ΔtnpA+Δorf13-lp-tet(M)+gamma delta+tnpX+ΔtnpR sequences. The Δorf13-lp-tet(M) sequence was a highly conserved genetic fragment in E. coli harboring tet(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 tet(M) among E. coli isolates.