Genetic characterization of novel class 1 Integrons In0, In1069 and In1287 to In1290, and the inference of In1069-associated integron evolution in Enterobacteriaceae

Dongguo Wang,Dongguo Wang,Jiao Feng,Dongsheng Zhou,Jiayu Chen,Kaiyu Zhou,Jianfeng Zhu,Liman Ma,Zhe Yin

doi:10.1186/s13756-017-0241-9

Abstract

BackgroundThis study aims to characterize genetically related class 1 integrons In1069, In893 and In1287 to In1290, and to further propose a scheme of stepwise integration or excision of individual gene cassettes (GCs) to generation of these integron variations.MethodsSix of 139 non-redundant Enterobacteriaceae strains were studied by bacterial antimicrobial susceptibility testing, detection of carbapenemase activity, and integron sequencing and sequence comparison.ResultsSix novel class 1 integrons, In0, In1069, and In1287 to In1290, together with the previously characterized In893, were determined from the above strains. An unusual blaKPC-2-carrying In0 and the blaIMP-30-carrying In1069 coexists in a single isolate of Escherichia coli. In0 contains a PcH1 promoter and a truncated aacA4’-3 gene cassette (GCaacA4’-3), as well as a blaKPC-2-containing region of Tn6296 integrated between PcH1 and GCaacA4’-3. In1069 carries GCblaIMP-30 and GCaacA4’-3 in this order. The other five integrons, In893 and In1287 to In1290, are genetically related to In1069, and all possess a core GCaacA4’-3. The integration or excision of one or more individual gene cassettes, such as GCblaIMP-30, GCaadA16, GCcatB3, GCarr3 and GCdfrA27, upstream or downstream of GCaacA4’-3 generates various gene cassettes arrays among these five integrons.ConclusionsThese findings provide the insight into stepwise and parallel evolution of In1069-associated integron variations likely under antibiotic selection pressure in clinical settings.

Highlights

This study aims to characterize genetically related class 1 integrons In1069, In893 and In1287 to In1290, and to further propose a scheme of stepwise integration or excision of individual gene cassettes (GCs) to generation of these integron variations
Class 1 integrons constitute a substantial reservoir of resistance genes that confer a selective advantage upon strong selection pressure imposed by human use of antimicrobial compounds, leading to the horizontal transfer of integron-carrying resistance markers from the community to hospitals and the development of multidrug resistance (MDR) among Enterobacteriaceae, independent of species or isolate origin [6,7,8]
The ancestors of class 1 integrons are not considered to be mobile elements, and the connection of class 1 integrons with Tn402 with a complete tniABQC transposition module generates a hybrid structure flanked by the 25 bp terminal inverted repeat initial (IRi) and inverted repeat terminal (IRt), making class 1 integrons capable of self-mobility [1,2,3]

Summary

Introduction

This study aims to characterize genetically related class 1 integrons In1069, In893 and In1287 to In1290, and to further propose a scheme of stepwise integration or excision of individual gene cassettes (GCs) to generation of these integron variations. Most class 1 integrons from clinical contexts carry modifications at their 5′ and 3′ ends, especially partial or complete deletions of the tniABQC module of Tn402, which impairs their mobility [4, 5]. These integrons are often inserted within mobile DNA elements such as plasmids and transposons, facilitating their rapid spread in the community and within hospitals [4, 5]

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