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Molecular characterization of trimethoprim resistance in Shigella sonnei in Sicily
A Agodi1, C Jones, E J Threlfall
1Institute of Hygiene and Preventive Medicine, University of Catania, Italy.
Abstract:
During the 3-year period 1985-7, all strains of Shigella sonnei isolated in Catania, Sicily, showed a high level of resistance to trimethoprim (Tp) which was invariably associated with resistance to other antibiotics. Plasmid analysis showed 18 different electropherotypes: 35 of 37 strains harboured a plasmid of 70 Megadaltons (MDa), and 29 of 37 strains a plasmid of 130 MDa. Restriction endonuclease fingerprinting of purified 70 MDa plasmid DNA from different strains demonstrated that these plasmids were similar but not identical. In some strains with transferable Tp resistance, DNA hybridization analysis demonstrated the presence of gene coding for the production of dihydrofolate reductase (DHFR) type V. In contrast, there was no detectable hybridization with DNA probes specific for genes coding for DHFR types I, II and IV. This is the first report of the DHFR type V gene outside Sri Lanka.
Insights
Shigella sonnei strains in Sicily showed high trimethoprim resistance linked to specific plasmids. This resistance was associated with the dihydrofolate reductase (DHFR) type V gene, newly reported outside Sri Lanka.
Area of Science:
- Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Shigella sonnei infections can lead to antibiotic resistance.
- Trimethoprim resistance in bacteria is a growing public health concern.
- Understanding the genetic basis of antibiotic resistance is crucial for effective treatment.
Purpose of the Study:
- To investigate the prevalence and genetic basis of trimethoprim resistance in Shigella sonnei strains from Catania, Sicily.
- To characterize the plasmids associated with trimethoprim resistance.
- To identify the specific dihydrofolate reductase (DHFR) gene type responsible for resistance.
Main Methods:
- Plasmid analysis using electropherotyping.
- Restriction endonuclease fingerprinting of plasmid DNA.
- DNA hybridization analysis using DHFR gene probes.
Main Results:
- All Shigella sonnei strains isolated between 1985-1987 exhibited high trimethoprim resistance.
- Most resistant strains harbored plasmids of 70 MDa and/or 130 MDa.
- DNA hybridization confirmed the presence of the DHFR type V gene in strains with transferable trimethoprim resistance, with no detectable DHFR types I, II, or IV.
Conclusions:
- The DHFR type V gene is associated with trimethoprim resistance in Shigella sonnei in Sicily.
- This finding represents the first report of the DHFR type V gene outside of Sri Lanka.
- The study highlights the importance of plasmid-mediated resistance mechanisms in the spread of antibiotic resistance.