Molecular diversity and conjugal transferability of class 2 integrons among escherichia coli isolates from food, animal and human sources

Autor: Torres Manrique, Carmen

Tipo de documento: Artículo de revista

Revista: International Journal of Antimicrobial Agents. ISSN: 0924-8579. Año: 2018.

doi 10.1016/j.ijantimicag.2018.02.001


Resumen: Integrons are genetic platforms able to excise, integrate and express antibiotic resistance gene cassettes. Here, we investigate the complete genetic organization, genetic environment, location and conjugative transferability of a collection of class 2 integrons carried by E. coli strains from different sources (poultry/pork-meat, animals, and humans). PCR cartography was conducted to determine the genetic arrangement of the integrons, their physical linkage to Tn7 and the chromosomal insertion at attTn7 site. Clonal relatedness of specific isolates was determined by MLST and OD-PCR. Transferability of class 2 integrons was tested by conjugation and the resulting transconjugants were characterized by antimicrobial resistance genotyping, S1-PFGE and replicon typing. Although a limited diversity of gene cassettes was shown, a high percentage of novel structures was identified due to the integration of insertion sequences at different sites (IS3/IS4/IS5/IS21 families). The insertion of an IS10 in the attI2 site of a class 2 integron, between Pc2B and Pc2C promoters, was likely mediated by a site-specific transposition event. Chromosomal insertion of the integrons at attTn7 was confirmed in 80% of the isolates. Conjugation experiments demonstrated that 29% of class 2 integrons could be mobilized to E. coli CHS26, demonstrating that they can be located in conjugative/mobilizable elements at a low frequency. Reported structures evidence how class 2 integrons have evolved by the activity of integron integrases and the invasion of ISs. Since most of them are chromosomally located, the dispersion is predominantly vertical, although conjugation events also contribute to the spread of class 2 integrons among bacterial communities.