Abstract
BackgroundVIM-type enzyme encodes the most widely acquired metallo-β-lactamases in Gram- negative bacteria. To obtain current epidemiological data for integrons from enterobacteriae in hospital, the study characterizes the genetic structure in In1059 by comparison with In846 integrons harbouring VIM gene and other class 1 integrons including In37, In62, In843 and In1021 with the aim of identifying the putative mechanisms involved integron mobilization and infer evolution of relevant integrons.MethodsSix of 69 recombinant plasmids from clinical strains were found to be class 1 integrons by digestion with BamHI, drug susceptibility testing, conjugation experiments, PCR amplification, integron cloning and sequencing, genome comparison, and detection of carbapenemase activity.ResultsThe sequences of the six recombinant plasmids encoding In1021, In843, In846, In37, In62, and the novel In1059 integron had approximate lengths of ~4.8-, 4.1-, 5.1-, 5.3-, 5.3- and 6.6- kb, respectively. The genetic structures of these integrons were mapped and characterized, and the carbapenemase activities of their parental strains were assessed.ConclusionsOur results suggest that the six variable integron structures and regular variations that exist in the gene cassettes provide a putative mechanism for the integron changes. Our study has also shown that the genetic features in the integrons named above fall within a scheme involving the stepwise and parallel evolution of class 1 integron variation likely under antibiotic selection pressure in clinical settings.
Highlights
VIM-type enzyme encodes the most widely acquired metallo-β-lactamases in Gram- negative bacteria
Integron cloning experiments and antibiotic susceptibility testing Six of 69 isolates, which resistance to aminoglycoside, quinolone, cephalosporin, and carbapenem antibiotics, from the clinical patients met the requirements of this study
Following BamHI digestion and ligation to a pMD19-T cloning vector, the recombinant plasmids were transformed into the competent cells, E. coli TOP10, by heat shock conversion, achieved the positive transformants which were selected by blue-white spot experiments, and sequenced
Summary
VIM-type enzyme encodes the most widely acquired metallo-β-lactamases in Gram- negative bacteria. The mechanisms of integration and excision of gene casettes are well described with integrations known to occur at attI × attC recombination sites [9, 10], and excisions requiring attC × attC recombination sites, Wang et al Antimicrobial Resistance and Infection Control (2017) 6:50 which occur in single-stranded sequences and activate the folded bottom strand [11, 12] Because of their linkage with transposons or being plasmid encoded, class 1 integrons can capture genetic structures, express gene cassettes, and facilitate their own mobility, but they are incapable of self-mobilization [5, 13]
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