title: Prevalence of tetracycline resistance genes and identification of tet(M) in clinical isolates of Escherichia coli from sick ducks in China.
abstract: Tetracycline resistance is one of the most frequently encountered resistance properties in bacteria of animal origin. The aim of the present study was to investigate the prevalence and diversity of tetracycline resistance (tet) genes among Escherichia coli clinical isolates from diseased ducks in China and to report the identification and sequencing of the tet(M) gene. The susceptibility of 85 Escherichia coli strains to tetracyclines was determined by broth microdilution, and the presence of tet genes was investigated by multiplex PCR. All of the 85 isolates were fully resistant to both oxytetracycline and tetracycline, and 76.5 % were resistant to doxycycline. Seventy-seven of the isolates (90.6 %) encoded multiple tet genes, with 17.6, 38.8 and 34.1 % encoding two, three and four tet genes, respectively, and only 7.1 % encoded a single tet(A) gene. The MICs of oxytetracycline and tetracycline for all isolates ranged from 16 to ≥128 µg ml(-1) with a MIC90 of >128 µg ml(-1), regardless of the type or number of tet genes encoded. Isolates containing tet(M) commonly had more than one tet gene per strain. The doxycycline resistance rate in the tet(M)-positive isolates was significantly higher than in the tet(M)-negative isolates (P<0.05). A full-length tet(M) gene, including the promoter region, was obtained by PCR in seven of the 41 tet(M)-positive isolates and was sequenced and cloned. The cloned tet(M) gene conferred resistance to tetracyclines in the recombinant Escherichia coli host strain. These results revealed that, in these isolates, the prevalence of multiple tet genes was strikingly high and that tet(M) played a role in doxycycline resistance.
authors.affiliation: College of Animal Husbandry and Veterinary Science, Henan Agricultural University, Zhengzhou 450002, PR China.
authors.forename: Gong-Zheng
authors.initials: GZ
authors.lastname: Hu
authors.affiliation: College of Animal Husbandry and Veterinary Science, Henan Agricultural University, Zhengzhou 450002, PR China.
authors.forename: Yu-Shan
authors.initials: YS
authors.lastname: Pan
authors.affiliation: College of Animal Husbandry and Veterinary Science, Henan Agricultural University, Zhengzhou 450002, PR China.
authors.forename: Hua
authors.initials: H
authors.lastname: Wu
authors.affiliation: Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou, Zhejiang, PR China.
authors.forename: Han
authors.initials: H
authors.lastname: Hu
authors.affiliation: College of Animal Husbandry and Veterinary Science, Henan Agricultural University, Zhengzhou 450002, PR China.
authors.forename: Rui
authors.initials: R
authors.lastname: Xu
authors.affiliation: College of Animal Husbandry and Veterinary Science, Henan Agricultural University, Zhengzhou 450002, PR China.
authors.forename: Li
authors.initials: L
authors.lastname: Yuan
authors.affiliation: College of Animal Husbandry and Veterinary Science, Henan Agricultural University, Zhengzhou 450002, PR China.
authors.forename: Jian-Hua
authors.initials: JH
authors.lastname: Liu
authors.affiliation: College of Animal Husbandry and Veterinary Science, Henan Agricultural University, Zhengzhou 450002, PR China.
authors.forename: Jian-Kun
authors.initials: JK
authors.lastname: Feng
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001715:Bird Diseases / Q000453:epidemiology* / Q000382:microbiology; D002681:China; D016384:Consensus Sequence; D004372:Ducks; D004926:Escherichia coli / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D015995:Prevalence; D012091:Repetitive Sequences, Nucleic Acid; D013752:Tetracycline / Q000494:pharmacology; D013753:Tetracycline Resistance / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D013752:Tetracycline