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Gut Pathog. 2013 Nov 19;5(1):34. doi: 10.1186/1757-4749-5-34.

ESBL-plasmids carrying toxin-antitoxin systems can be "cured" of wild-type Escherichia coli using a heat technique.

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1
Centre for Infection Medicine, Institute of Microbiology and Epizootics, Freie Universität Berlin, Robert von Ostertag-Str, 7-13, Berlin 14136, Germany. katharina.schaufler@fu-berlin.de.

Abstract

BACKGROUND:

Plasmid-encoded extended-spectrum beta-lactamase (ESBL)-enzymes are frequently produced by Escherichia coli. Several ESBL-plasmids contain genes for toxin-antitoxin (TA) systems, which assure the maintenance of plasmids in bacteria and prevent the cells from "post-segregational killing". These systems limit options to "cure" plasmids of ESBL-wild-type strains due to the death of the bacterial cells. A helpful tool to understand the role of ESBL-plasmids in the dissemination of pandemic multi-resistant E. coli are ESBL-plasmid-"cured"-variants (PCVs) and their comparison to ESBL-wild-type strains. The purpose of this study was to construct PCVs of ESBL-wild-type E. coli strains despite the presence of genes for TA systems.

FINDINGS:

Using enhanced temperatures and brain-heart-infusion broth it was possible to construct viable PCVs of wild-type ESBL-E. coli strains. The occurrence of TA system-genes including hok/sok, srnB/C, vagC/D, pemI/K on ESBL-plasmids of replicon types FIA or FIB was demonstrated by bioinformatic analyses. The loss of the plasmid and the genetic identity of PCV and corresponding wild-type strain was confirmed via different methods including plasmid-profile-analysis, pulsed-field gel electrophoresis and bioinformatics using generated whole genome data of the strains.

CONCLUSIONS:

This short report describes the successful construction of viable PCVs of ESBL-wild-type E. coli strains. The results are hence surprising due to the fact that all "cured" ESBL-plasmids contained at least one complete toxin-antitoxin system, whose loss would normally mean the death of bacterial cells.

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