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Tn3 as the molecular basis of ampicillin resistance in E. coli--an epidemiological survey
Abstract:
Plasmids of 31 E. coli strains coding for the TEM-1 beta-lactamase were analysed for the molecular basis of this enzyme. In transposition experiments we could demonstrate that only 50% of the plasmids were able to transpose their ampicillin-resistance gene. Two of the non-transposing structures were further examined. The 8.1 kb plasmid pBP738 contained Tn3 having suffered a point mutation within the transposase gene that could be complemented by an intact transposase. The 79 kb plasmid pBP749 carried a TEM-1 coding sequence, but the homology with Tn3 was limited to 1.18 kb.
Insights
Researchers investigated the molecular basis of TEM-1 beta-lactamase in E. coli plasmids. Only half of the plasmids could transpose their ampicillin-resistance gene, with specific mutations identified in non-transposing plasmids.
Area of Science:
- Molecular biology
- Microbiology
- Genetics
Background:
- The TEM-1 beta-lactamase enzyme confers resistance to beta-lactam antibiotics in bacteria.
- Understanding the genetic elements controlling beta-lactamase gene expression and mobility is crucial for combating antibiotic resistance.
Purpose of the Study:
- To analyze the molecular basis of TEM-1 beta-lactamase in 31 E. coli strains.
- To investigate the transposition capabilities of plasmids carrying the TEM-1 beta-lactamase gene.
Main Methods:
- Plasmid DNA analysis from 31 E. coli strains.
- Transposition experiments to assess gene mobility.
- Molecular characterization of non-transposing plasmids, including sequencing and complementation assays.
Main Results:
- Only 50% of the analyzed plasmids successfully transposed their ampicillin-resistance gene.
- Plasmid pBP738 contained a point mutation in the transposase gene of Tn3, which was complementable.
- Plasmid pBP749 harbored a TEM-1 coding sequence with limited homology to Tn3.
Conclusions:
- The ability of TEM-1 beta-lactamase encoding plasmids to transpose varies significantly.
- Specific genetic defects, such as mutations in transposase genes or altered structural homology, can impair plasmid transposition.
- These findings highlight the complex molecular mechanisms underlying the spread of antibiotic resistance genes.