Abstract
BACKGROUND: 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. METHODS: Six of 139 non-redundant Enterobacteriaceae strains were studied by bacterial antimicrobial susceptibility testing, detection of carbapenemase activity, and integron sequencing and sequence comparison. RESULTS: Six novel class 1 integrons, In0, In1069, and In1287 to In1290, together with the previously characterized In893, were determined from the above strains. An unusual bla(KPC-2)-carrying In0 and the bla(IMP-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 bla(KPC-2)-containing region of Tn6296 integrated between PcH1 and GCaacA4'-3. In1069 carries GCbla(IMP-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 GCbla(IMP-30), GCaadA16, GCcatB3, GCarr3 and GCdfrA27, upstream or downstream of GCaacA4'-3 generates various gene cassettes arrays among these five integrons. CONCLUSIONS: These findings provide the insight into stepwise and parallel evolution of In1069-associated integron variations likely under antibiotic selection pressure in clinical settings.