HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Díaz-Mejía, J. J. Articles by Souza, V. Search for Related Content PubMed PubMed Citation Articles by Díaz-Mejía, J. J. Articles by Souza, V. Agricola Articles by Díaz-Mejía, J. J. Articles by Souza, V.

An analysis of the evolutionary relationships of integron integrases, with emphasis on the prevalence of class 1 integrons in Escherichia coli isolates from clinical and environmental origins

¹ Fundación Lusara, Apartado Postal 102-006, 08930, Mexico City, Mexico
² Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Av. Universidad 2001, Col. Chamilpa, 62210 Cuernavaca, Morelos, Mexico
³ Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Circuito Exterior, 04510, Mexico City, Mexico
⁴ Instituto de Ecología, Universidad Nacional Autónoma de México, Circuito Exterior, 04510, Mexico City, Mexico

Correspondence
Carlos F. Amábile-Cuevas
carlos.amabile{at}lusara.org

Integrons are genetic elements that allow the mobilization and expression of smaller elements called gene cassettes, and are considered to be key elements in the evolution of antibiotic resistance among enteric bacteria. Although in nature integrons appear to be abundant, the presence of class 1 integrons in Escherichia coli has been reported to be much less frequent among isolates of non-human origin than among clinical ones. Searching for integrons in a wide variety of E. coli isolates we found a steep decline in class 1 integron prevalence when going from clinical strains to environmental ones, from outdoor urban dust to the microbiota of wild animals. Attempting to assess the causes of this decline, we addressed the evolution of integron integrases, comparing the amino acid sequence of various of these enzymes, the key proteins in gene-cassette mobilization. We found that all integrases are homologues, but different classes have been recruited by enteric bacteria, supporting the notion that integrons can frequently be gained and lost. Additionally, we found that phylogenetically distant organisms that bear intI1, such as E. coli and other enteric bacteria, but also the Gram-positive corynebacteria, have a similar preferential genomic codon usage (CU), suggesting that CU might play an important role in the acquisition and/or maintenance of integrons. In fact, the CU of intI1 is more similar to the preferential genomic CU of non-enteric bacteria than it is to that of E. coli. CU has been proposed to be involved in the retention of horizontally transferred genes; integrons in E. coli are often plasmid-borne. This might explain the reduced prevalence of integrons in enteric bacteria when not under the selective pressure of antibiotics. Collectively, our results provide evidence that class 1 integrons are important gene mobilizers within E. coli, but are not acquired and/or stably maintained without selective pressure. Thus, although not effective to reduce the prevalence of resistance itself, decreasing the use of antibiotics could be useful to diminish the presence of gene-mobilization machineries.