Novel Insights about Class 2 Integrons from Experimental and Genomic Epidemiology

Abstract

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 intI2 gene from 130 of 726 isolates, most of which were clinical isolates, and only 1 (a psychrophilic Pseudomonas sp.) was from a water sample. Unlike the widespread distribution of class 1 integrons within Gram-negative bacilli, only Acinetobacter baumannii and Enterobacter cloacae 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 Tn7, the genetic platform in which class 2 integrons have always been reported, showed tns modules with a mosaic genetic structure. A bioinformatic analysis performed with the tns genes present in sequence databases, the finding of intI2 not associated with tns genes, and the genetic examination of novel tns-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 Tn7 transposons.

Prevalence of integrons and Antimicrobial Resistance Genes Among Clinical Isolates of Enterobacter spp. From Hospitals of Tehran

“…The ability of integrons to integrate resistance gene cassettes makes them prime pools for the further dissemination of antibiotic resistance among clinical isolates of gram-negative bacteria, including Enterobacter isolates (13). Our findings indicated that the 41 % of isolated Enterobacter were integron positive, this rate of integron positive in our isolates are similar with published reports that Enterobacter harbors high prevalence of integron class 1, lower class 2 and no class 3 (14)(15)(16). Of course, in study in France a new class 3 integron, In3-5, detected in an Enterobacter cloacae isolate retrieved from a random French hospital effluent sample (17).…”

Role of integrons in antimicrobial resistance: A review

“…In a previous study conducted on 726 isolates, 130 of which harbored class 2 integron and only Acinetobacter baumannii and Enterobacter cloacae strains at a high frequency (Ramírez MS, 2010). In Serratia marcescens, 9 out of 30 (30.0%) were positive for class 2 integron, with identical dfrA1-sat1-aadA1 cassette arrays (Crowley, 2008).…”

Integrons: Past, Present, and Future

“…It is therefore not surprising that their cassette arrays are highly conserved (160) and that their range of cassette functions is much more limited than those of class 1 integrons (161)(162)(163). There are some variant cassette arrays described, and it is thought that these cassette rearrangements were mediated by integrase activity in trans or by suppression of the internal stop codon.…”