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Detection of Horizontal Gene Transfer Mediated by Natural Conjugative Plasmids in E. coli
Published on: March 24, 2023
Different IncI1 plasmids from Escherichia coli carry ISEcp1-blaCTX-M-15 associated with different Tn2-derived
Zhiyong Zong1, Andrew N Ginn2, Hana Dobiasova3
1Centre for Infectious Diseases and Microbiology, Westmead Millennium Institute, The University of Sydney and Westmead Hospital, Westmead, NSW 2145, Australia; Department of Infectious Diseases, West China Hospital, Sichuan University, Chengdu, China.
Abstract:
The bla(CTX-M-15) gene, encoding the globally dominant CTX-M-15 extended-spectrum β-lactamase, has generally been found in a 2.971-kb ISEcp1-bla(CTX-M-15)-orf477Δ transposition unit, with ISEcp1 providing a promoter. In available IncF plasmid sequences from Escherichia coli, this transposition unit interrupts a truncated copy of transposon Tn2 that lies within larger multiresistance regions. In E. coli, bla(CTX-M-15) is also commonly associated with IncI1 plasmids and here three such plasmids from E. coli clinical isolates from western Sydney 2006-2007 have been sequenced. The plasmid backbones are organised similarly to those of other IncI1 plasmids, but have insertions and/or deletions and sequence differences. Each plasmid also has a different insertion carrying bla(CTX-M-15). pJIE113 (IncI1 sequence type ST31) is almost identical to plasmids isolated from the 2011 E. coli O104:H4 outbreak in Europe, where the typical bla(CTX-M-15) transposition unit interrupts a complete Tn2 inserted directly in the plasmid backbone. In the novel plasmid pJIE139 (ST88), ISEcp1-blaC(TX-M-15)-orf477Δ lies within a Tn2/3 hybrid transposon. Homologous recombination could explain movement of ISEcp1-bla(CTX-M-15)-orf477Δ between copies of Tn2 on IncF and IncI1 plasmids and generation of the Tn2/3 hybrid. pJIE174 (ST37) is almost identical to pESBL-12 from the Netherlands and in these plasmids bla(CTX-M-15) is flanked by two copies of IS26 that truncate the transposition unit within a larger region bounded by the ends of Tn2. bla(CTX-M-15) and the associated ISEcp1-derived promoter may be able to move from this structure by the actions of IS26, independently of both ISEcp1 and Tn2.
Insights
The bla(CTX-M-15) gene, responsible for CTX-M-15 extended-spectrum beta-lactamase, shows varied integration into IncI1 plasmids in E. coli. Different insertion mechanisms, including IS26 elements, facilitate its mobility and spread.
Area of Science:
- Molecular Biology
- Genetics
- Antimicrobial Resistance
Background:
- The bla(CTX-M-15) gene encodes the globally prevalent CTX-M-15 extended-spectrum beta-lactamase (ESBL).
- This gene is typically found within an ISEcp1-bla(CTX-M-15)-orf477Δ transposition unit, with ISEcp1 providing promoter activity.
- In Escherichia coli, bla(CTX-M-15) is associated with both IncF and IncI1 plasmids, often within larger multiresistance regions.
Purpose of the Study:
- To investigate the genetic context and integration patterns of the bla(CTX-M-15) gene in IncI1 plasmids from E. coli clinical isolates.
- To characterize the specific transposition units and surrounding genetic elements associated with bla(CTX-M-15) in these plasmids.
- To explore potential mechanisms of bla(CTX-M-15) gene mobilization and dissemination among different plasmid types.
Main Methods:
- Whole-genome sequencing of three IncI1 plasmids (pJIE113, pJIE139, pJIE174) from E. coli clinical isolates.
- Comparative sequence analysis of plasmid backbones and inserted genetic elements.
- Identification and characterization of transposition units, transposons (Tn2, Tn2/3 hybrid), and insertion sequences (ISEcp1, IS26).
Main Results:
- The IncI1 plasmid backbones showed organizational similarities to known IncI1 plasmids but with unique insertions and deletions.
- Each sequenced plasmid contained a distinct insertion carrying bla(CTX-M-15): pJIE113 showed a complete Tn2 insertion, pJIE139 contained a Tn2/3 hybrid transposon, and pJIE174 had bla(CTX-M-15) flanked by IS26 elements.
- Sequence similarities were observed between pJIE113 and outbreak-associated plasmids, suggesting horizontal gene transfer.
Conclusions:
- The bla(CTX-M-15) gene exhibits diverse integration strategies within IncI1 plasmids, differing from its common IncF plasmid context.
- Homologous recombination and the action of insertion sequences like IS26 likely play significant roles in the mobility and evolution of bla(CTX-M-15) carrying elements.
- Understanding these genetic mechanisms is crucial for tracking the spread of ESBL-producing E. coli.
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