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Distribution and genetic location of Tn7 in trimethoprim-resistant Escherichia coli
Abstract:
A series of 178 strains of Escherichia coli, highly resistant to trimethoprim, isolated from hospital patients and patients in the community between 1979 and 1983, was examined for the presence of Tn7 on a plasmid or on the chromosome only, by transposition to RP4 and restriction endonuclease digestion with Hind III. Of the isolates, 57% carried Tn7. Comparison of hospital isolates from 1979 to 1980 and 1982 showed that although the proportions that carried Tn7 were similar (63% and 57%) there had been a significant change in the genetic location of the transposon. The proportion of plasmid-mediated Tn7 had fallen from 62% to 30% with a corresponding rise in Tn7 located exclusively on the chromosome from 38% to 70%. This change may be the result of continuing transposition of Tn7 from plasmids to the bacterial chromosome followed by plasmid loss. The consequent reduction in the mobility of trimethoprim-resistance genes may in turn lead to changes in the incidence of resistance.
Insights
Trimethoprim resistance in Escherichia coli is often linked to the Tn7 genetic element. Over time, Tn7 has increasingly moved from plasmids to the bacterial chromosome, potentially impacting resistance spread.
Area of Science:
- Microbiology
- Genetics
- Antimicrobial Resistance
Background:
- Trimethoprim resistance in Escherichia coli is a significant public health concern.
- The Tn7 transposon is a key genetic element associated with trimethoprim resistance.
Purpose of the Study:
- To investigate the genetic location of the Tn7 element in trimethoprim-resistant Escherichia coli strains.
- To analyze changes in Tn7's location over time in hospital and community isolates.
Main Methods:
- Analysis of 178 Escherichia coli strains isolated between 1979 and 1983.
- Transposition to RP4 and restriction endonuclease digestion with Hind III to determine Tn7 location.
- Comparison of genetic location in isolates from different time periods.
Main Results:
- 57% of the examined Escherichia coli isolates carried the Tn7 element.
- A significant shift in Tn7's genetic location was observed between 1979-1980 and 1982.
- The proportion of plasmid-mediated Tn7 decreased from 62% to 30%, while chromosomal Tn7 increased from 38% to 70%.
Conclusions:
- Transposition of Tn7 from plasmids to the chromosome, followed by plasmid loss, likely explains the observed shift.
- Reduced mobility of trimethoprim-resistance genes due to chromosomal localization may alter resistance incidence.
- Understanding Tn7 dynamics is crucial for managing antimicrobial resistance in Escherichia coli.