AUTHOR=Sun Ya-wei , Liu Ying-ying , Wu Hua , Wang Ling-fei , Liu Jian-hua , Yuan Li , Pan Yu-shan , He Dan-dan , Hu Gong-zheng 

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

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.03168

DOI=10.3389/fmicb.2018.03168

ISSN=1664-302X

ABSTRACT=<p>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 <italic>Escherichia coli</italic>. In the current study, conjugation experiments were performed between seven different tetracycline-resistant, azide-susceptible <italic>E. coli</italic> strains isolated from ducks and tetracycline-sensitive, azide-resistant <italic>E.coli</italic> J53. Transconjugants were obtained from two of the strains at a frequency of 1.2 × 10<sup>−8</sup>. PCR, southern blotting and sequencing demonstrated that <italic>tet</italic>(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<italic>tnpA</italic>+Δ<italic>orf13</italic>-<italic>lp</italic>-<italic>tet</italic>(M)+gamma delta+<italic>tnpX</italic>+Δ<italic>tnpR</italic> sequences. The Δ<italic>orf13</italic>-<italic>lp</italic>-<italic>tet</italic>(M) sequence was a highly conserved genetic fragment in <italic>E. coli</italic> harboring <italic>tet</italic>(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 <italic>tet</italic>(M) among <italic>E. coli</italic> isolates.</p>