Novel Insights about Class 2 Integrons from Experimental and Genomic Epidemiology

<jats:title>ABSTRACT</jats:title> <jats:p> In order to contribute to the knowledge of the architecture and epidemiology of class 2 integrons, we performed a class 2 integron molecular survey in which we analyzed 726 isolates in two bacterial populations from environmental and nonepidemiologically related clinical samples, respectively, collected from 1982 to 2007. We recovered the <jats:italic>intI2</jats:italic> gene from 130 of 726 isolates, most of which were clinical isolates, and only 1 (a psychrophilic <jats:italic>Pseudomonas</jats:italic> sp.) was from a water sample. Unlike the widespread distribution of class 1 integrons within Gram-negative bacilli, only <jats:italic>Acinetobacter baumannii</jats:italic> and <jats:italic>Enterobacter cloacae</jats:italic> harbored class 2 integrons at a high frequency in our collection. Class 2 integrons with six novel cassette arrays were documented. Characterization of the transposition module of Tn <jats:italic>7</jats:italic> , the genetic platform in which class 2 integrons have always been reported, showed <jats:italic>tns</jats:italic> modules with a mosaic genetic structure. A bioinformatic analysis performed with the <jats:italic>tns</jats:italic> genes present in sequence databases, the finding of <jats:italic>intI2</jats:italic> not associated with <jats:italic>tns</jats:italic> genes, and the genetic examination of novel <jats:italic>tns</jats:italic> -like genes found in three isolates indicated the possibility of the independent evolution of the two components related to horizontal gene transfer, the class 2 integrons and the Tn <jats:italic>7</jats:italic> transposons. </jats:p>