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Preparation of Multifunctional Silk-Based Microcapsules Loaded with DNA Plasmids Encoding RNA Aptamers and Riboswitches
Published on: October 8, 2021
Molecular characterization of plasmid-encoded Tripoli MBL 1 (TMB-1) in Enterobacteriaceae
Lauraine Gauthier1,2,3, Laurent Dortet1,2,3, Agnès B Jousset1,2,3
1Bactériologie-Hygiène Unit, Bicêtre Hospital, APHP, Le Kremlin-Bicêtre, France.
Objectives:
Available commercial tools (molecular methods or immunochromatographic assays) usually allow the detection of the five most prevalent carbapenemases (KPC, NDM, VIM, IMP and OXA-48-like), but miss minor carbapenemases. Here, we characterize two enterobacterial isolates with reduced susceptibility to carbapenems and negative for the most commonly encountered carbapenemase genes.
Methods:
Enterobacter hormaechei and Citrobacter freundii isolates were recovered from a bile sample and rectal screening, respectively. Both isolates were investigated by WGS. Resistance genes were detected using ResFinder. The blaTMB-1-harbouring plasmid was reconstructed using CLC genomic workbench 10.0 and was annotated using the RAST tool. Transfer frequency was determined by conjugation experiments using the laboratory strain Escherichia coli J53.
Results:
The two isolates were resistant to broad-spectrum cephalosporins and carbapenems. WGS revealed the presence of blaTMB-1, which has previously only been described in non-fermenters. blaTMB-1 was located within an ISKpn19-based composite class 1 transposon. Comparative genomics revealed that this structure was carried on a conjugative IncN-type plasmid within an integration hotspot. Conjugation experiments revealed high transfer frequencies of ∼1 × 10-3.
Conclusions:
To the best of our knowledge, this study corresponds to the first report of Tripoli MBL 1-producing Enterobacteriaceae. Despite always being described as likely to be chromosomally located in non-fermenters, the blaTMB-1 gene is now found to be carried by a conjugative plasmid among Enterobacteriaceae, raising concern about the possible dissemination of this carbapenemase. The blaTMB-1 gene should now be suspected when PCRs targeting the main carbapenemases remain negative.
Insights
This study identifies the blaTMB-1 carbapenemase gene in Enterobacteriaceae, which is typically found in non-fermenters. The gene is plasmid-borne and highly transferable, raising concerns about its spread.
Area of Science:
- Microbiology
- Genetics
- Antimicrobial Resistance
Background:
- Commercial diagnostic tools often miss less common carbapenemase genes.
- Enterobacteriaceae are significant human pathogens.
- Carbapenem resistance poses a major public health threat.
Purpose of the Study:
- To characterize novel carbapenemase genes in Enterobacteriaceae.
- To investigate the genetic basis of carbapenem resistance in clinical isolates.
- To assess the transferability of newly identified resistance genes.
Main Methods:
- Whole-genome sequencing (WGS) of clinical isolates.
- Gene identification using ResFinder.
- Plasmid reconstruction and annotation.
- Conjugation experiments to determine gene transfer frequency.
Main Results:
- Identified blaTMB-1 gene in Enterobacter hormaechei and Citrobacter freundii.
- The blaTMB-1 gene was located on a conjugative IncN-type plasmid within a transposon.
- High transfer frequency (approximately 1x10^-3) of the blaTMB-1 gene was observed.
Conclusions:
- This is the first report of blaTMB-1 in Enterobacteriaceae.
- The plasmid-borne blaTMB-1 gene can disseminate among Enterobacteriaceae.
- blaTMB-1 should be suspected in carbapenem-resistant Enterobacteriaceae when common carbapenemase genes are absent.
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