title: Detection and linkage to mobile genetic elements of tetracycline resistance gene tet(M) in Escherichia coli isolates from pigs.
abstract: BACKGROUND
  In Escherichia coli the genes involved in the acquisition of tetracycline resistance are mainly tet(A) and tet(B). In addition, tet(M) is the most common tetracycline resistance determinant in enterococci and it is associated with conjugative transposons and plasmids. Although tet(M) has been identified in E. coli, to our knowledge, there are no previous reports studying the linkage of the tet(M) gene in E. coli to different mobile genetic elements. The aim of this study was to determine the occurrence of tet(A), tet(B), and tet(M) genes in doxycycline-resistant E. coli isolates from pigs, as well as the detection of mobile genetic elements linked to tet(M) in E. coli and its possible transfer from enterococci.
  
  
  RESULTS
  tet(A) was the most frequently detected gene (87.9%) in doxycycline-resistant isolates. tet(M) was found in 13.1% E. coli isolates. The tet(M) gene was detected in relation with conjugative transposons in 10 out of 36 enterococci isolates analyzed but not in any of E. coli isolates positive for tet(M). Southern blot showed that in E. coli and in most of the enterococci isolates the tet(M) gene was carried on a plasmid. According to the phylogenetic analysis, E. coli contained a new tet(M) allele grouping separately. Mating experiments revealed that tet(M) was carried on a mobile element successfully transferred between enterococci and between enterococci and E. coli.
  
  
  CONCLUSIONS
  The detection of tet(M) in E. coli isolates from pigs was higher than expected. In our study, tet(M) detected in E. coli seems not to have been transferred from enterococci, although it can not be ruled out that the horizontal transfer of this gene occurred from other intestinal tract bacteria.
authors.forename: Sonia
authors.initials: S
authors.lastname: Jurado-Rabadán
authors.forename: Ricardo
authors.initials: R
authors.lastname: de la Fuente
authors.affiliation: Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain. ruizsanta@vet.ucm.es.
authors.forename: José A
authors.initials: JA
authors.lastname: Ruiz-Santa-Quiteria
authors.forename: José A
authors.initials: JA
authors.lastname: Orden
authors.forename: Lisbeth E
authors.initials: LE
authors.lastname: de Vries
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Agersø
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D008040:Genetic Linkage; D020071:Interspersed Repetitive Sequences / Q000235:genetics*; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology*; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C083138:Tet M resistance protein, Bacteria; D013752:Tetracycline