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Vol. 20. Núm. 7.
Páginas 341-345 (Agosto 2002)
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Vol. 20. Núm. 7.
Páginas 341-345 (Agosto 2002)
DOI: 10.1016/S0213-005X(02)72813-9
Acceso a texto completo
Estructura y función de los integrones
Structure and function of integrons
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Montserrat Sabaté, Guillem Prats1
Autor para correspondencia
gprats@cs.vhebron.es

Correspondencia: Dr. G. Prats. Dirección actual: Servicio de Microbiología. Hospital de la Vall d’Hebron. P.° Vall d’Hebron, s/n. 08035 Barcelona. España.
Servicio de Microbiología. Hospital de la Santa Creu i Sant Pau. Universitat Autònoma de Barcelona. España
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Resumen
Bibliografía
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Estadísticas

Los integrones son unas piezas genéticas que han despertado gran interés porque algunos de ellos vehiculan genes de resistencia a los antimicrobianos. Desde el extremo 5’ al 3’ están formados por un fragmento que codifica una integrasa (intI) y a continuación una secuencia attI a la que se unen los genes de resistencia. Dentro de intI, en su extremo 3’, hay una secuencia promotora Pant a partir de la cual se transcriben los genes de resistencia integrados, ya que estos genes carecen de promotor.

En efecto, la integrasa reconoce en ciertos genes de resistencia (denominados genes casete) una secuencia específica denominada 59-be, que une, por recombinación, a la secuencia attI del integrón. El fragmento formado por intI-attI está altamente conservado en todos los integrones y se denomina 5’-CS.

Los integrones se han clasificado según la secuencia de su integrasa. Los detectados con más frecuencia en cepas aisladas en clínica pertenecen a la clase 1. Los integrones de la clase 1 están formados por el 5’-CS y a continuación se sitúan los diferentes genes casetes captados, por lo que constituye una zona variable y, finalmente, hay una zona conservada denominada 3’-CS formada por 2 genes uno de resistencia a compuestos de amonio cuaternario (qacEδI) y otro a sulfamidas (sul1); estos 2 genes, no son casetes y, por lo tanto, no son móviles sino fijos. La estructura de uno de estos integrones vendría representada por IntI-attI [R1+R2+…]-qacEδ1-sul1.

Probablemente, los integrones no son móviles por sí mismos, pero con frecuencia se hallan en transposones que a su vez se encuentran en plásmidos conjugativos, por lo que su movilidad horizontal está asegurada, como se constata por su amplia difusión entre las bacterias.

Palabras clave:
Integrones
Resistencia
Antimicrobianos

Integrons are genetic elements known for their role in the acquisition and expression of genes conferring antibiotic resistance. Integrons have an integrase gene (intI), an attachment site (attI), into which individual resistance genes are inserted and a promotor sequence (Pant), allowing expression of resistance genes (cassette-associated genes), which do not have promotors. Integrase recognizes 59-be, a specific sequence in certain resistance genes, which is captured by recombination at the attI attachment site. The fragment intI - attI is highly conserved in all integrons and is called 5’-CS.

Integrons have been classified according to the sequence of their integrase and the ones most frequently detected in isolated clinical strains belong to Class I. Class I integrons contain the 5’-CS region followed by gene cassettes in a variable region and finally, a conserved region known as 3’-CS containing two genes, the quaternary ammonium resistance gene (qacEδI) and the sulphonamide resistance gene (sul1); both genes are fixed in this structure. Accordingly, the structure of a Class 1 integron would be IntI - attI [R1+R2+…] - qacEδ1 - sul1.

Integrons are probably not mobile, but they are often found in transposons within conjunctive plasmids, which assures their mobility, as can be seen by their wide diffusion among bacteria.

Keywords:
Integrons
Resistance
Antimicrobials
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Bibliografía
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Copyright © 2002. Elsevier España, S.L.. Todos los derechos reservados
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