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Resistance to piperacillin/tazobactam in Escherichia coli resulting from extensive IS26-associated gene amplification of blaTEM-1

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BACKGROUND: bla TEM-1 encodes a narrow-spectrum β-lactamase that is inhibited by β-lactamase inhibitors and commonly present in Escherichia coli. Hyperproduction of blaTEM-1 may cause resistance to penicillin/β-lactamase inhibitor (P/BLI) combinations.

OBJECTIVES: To characterize EC78, an E. coli bloodstream isolate, resistant to P/BLI combinations, which contains extensive amplification of blaTEM-1 within the chromosome.

METHODS: EC78 was sequenced using Illumina and Oxford Nanopore Technology (ONT) methodology. Configuration of blaTEM-1 amplification was probed using PCR. Expression of blaTEM-1 mRNA was determined using quantitative PCR and β-lactamase activity was determined spectrophotometrically in a nitrocefin conversion assay. Growth rate was assessed to determine fitness and stability of the gene amplification was assessed by passage in the absence of antibiotics.

RESULTS: Illumina sequencing of EC78 identified blaTEM-1B as the only acquired β-lactamase preceded by the WT P3 promoter and present at a copy number of 182.6 with blaTEM-1B bracketed by IS26 elements. The chromosomal location of the IS26-blaTEM-1B amplification was confirmed by ONT sequencing. Hyperproduction of blaTEM-1 was confirmed by increased transcription of blaTEM-1 and β-lactamase activity and associated with a significant fitness cost; however, the array was maintained at a relatively high copy number for 150 generations. PCR screening for blaTEM amplification of isolates resistant to P/BLI combinations identified an additional strain containing an IS26-associated amplification of a blaTEM gene.

CONCLUSIONS: IS26-associated amplification of blaTEM can cause resistance to P/BLI combinations. This adaptive mechanism of resistance may be overlooked if simple methods of genotypic prediction (e.g. gene presence/absence) are used to predict antimicrobial susceptibility from sequencing data.

TidsskriftThe Journal of antimicrobial chemotherapy
Udgave nummer11
Sider (fra-til)3179-3183
Antal sider5
StatusUdgivet - 1 nov. 2019

Bibliografisk note

© The Author(s) 2019. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email:

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