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Updated: Feb 27, 2026
Detection of Horizontal Gene Transfer Mediated by Natural Conjugative Plasmids in E. coli
Published on: March 24, 2023
IncX3 plasmid mediated occurrence of blaNDM-4 within Escherichia coli ST448 from India
Nargis A Choudhury1, Deepjyoti Paul1, Atanu Chakravarty2
1Department of Microbiology, Assam University, Silchar, India.
Abstract:
This study was designed to investigate blaNDM-4 encoded within IncX3 type plasmid and their copy number alteration under carbapenem pressure within clinical isolates of Escherichia coli. NDM-4 producing E. coli isolates were collected from an Indian hospital and transferability as well as plasmid incompatibility typing was determined. Genetic environment and antibiogram profiling was carried out. Quantitative Real Time PCR was done to determine the change in plasmid copy number under concentration gradient carbapenem stress. Multilocus sequence typing and pulsed field gel electrophoresis was performed for typing of isolates. Four multidrug resistant isolates were found to harbour transconjugable blaNDM-4 carrying within IncX3 type plasmid. The blaNDM-4 was flanked by insertion sequences ISAba125 and IS5 in the upstream region whereas bleMBL was present in the downstream area. Copy number results indicated that the blaNDM-4 gene was maintained high in plasmid under exposure of ertapenem. All the strains belonged to ST448 and PFGE analysis revealed three different pulsotypes. This is the first report of blaNDM-4 encoded IncX3 type plasmid in E. coli of ST448 and needs a systematic screening policy to rapid detection of NDM-4 poducing strains to prevent dissemination of this resistant determinant in future.
Insights
This study found that the blaNDM-4 gene, conferring carbapenem resistance in Escherichia coli, is located on an IncX3 plasmid. Carbapenem pressure maintained high plasmid copy numbers, suggesting a mechanism for resistance spread.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Carbapenem resistance poses a significant global health threat, particularly in Gram-negative bacteria like Escherichia coli.
- The New Delhi metallo-beta-lactamase (NDM) enzyme confers resistance to a broad spectrum of beta-lactam antibiotics, including carbapenems.
- IncX3 plasmids are known to carry various antibiotic resistance genes and are frequently observed in Enterobacteriaceae.
Purpose of the Study:
- To investigate the blaNDM-4 gene within IncX3 plasmids in clinical Escherichia coli isolates.
- To determine the copy number alteration of these plasmids under carbapenem pressure.
- To analyze the genetic environment and epidemiological characteristics of NDM-4 producing E. coli.
Main Methods:
- Plasmid transferability and incompatibility typing.
- Antibiogram profiling and genetic environment analysis.
- Quantitative Real-Time PCR for plasmid copy number determination.
- Multilocus Sequence Typing (MLST) and Pulsed Field Gel Electrophoresis (PFGE) for isolate typing.
Main Results:
- Four multidrug-resistant E. coli isolates harbored transconjugable blaNDM-4 on IncX3 plasmids.
- The blaNDM-4 gene was located between insertion sequences ISAba125 and IS5, with bleMBL downstream.
- Carbapenem exposure (ertapenem) maintained high plasmid copy numbers.
- All isolates belonged to Sequence Type 448 (ST448) and showed three distinct PFGE pulsotypes.
Conclusions:
- This is the first report of blaNDM-4 on an IncX3 plasmid in E. coli ST448.
- The ability of carbapenems to increase plasmid copy number may facilitate the dissemination of NDM-4.
- Systematic screening for NDM-4 producing strains is crucial to prevent further spread of this resistance determinant.
