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Molecular characterization of trimethoprim resistance in salmonellas isolated in Sicily, 1985-1988
A Agodi1, M Marranzano, C S Jones
1Institute of General Biology, University of Catania, Sicily, Italy.
Abstract:
The occurrence of trimethoprim (Tp) resistance in salmonellas isolated from humans and water samples in Sicily between 1985 and 1988 has been investigated and the Tp resistance mechanisms have been further characterized on the basis of hybridization with probes for the dihydrofolate reductase (DHFR) genes types I, II, IV and V. Of 765 strains examined, high level (> 1000 mg/l) resistance to Tp was identified in 23 strains (3%). In 22 of these strains, such resistance was associated with resistance to sulphonamides. Six serovars with Tp-resistant strains were identified, Salmonella typhimurium (14 strains), S. enteridis (2), S. agona (2), S. mbandaka (2), S. virchow (2), S. indiana (1). In all strains with high level Tp resistance, resistance to this antimicrobial was plasmid-encoded, in most strains by plasmids with MWs ranging from 70-100 MDa. On the basis of restriction endonuclease analysis, four different categories of Tp resistance plasmids were identified in Tp-resistant strains of S. typhimurium. Hybridization with the DHFR I probe was observed in three strains of Tp-resistant S. typhimurium and two strains of Tp-resistant S. enteritidis; in contrast, in none of the strains tested was there any detectable hybridization with the probes for DHFR types II, IV and V. It is concluded that the DHFR type I resistance mechanism, common in Tp-resistant enterobacteria in many European countries, is relatively uncommon in Tp-resistant salmonellas isolated in Sicily. Furthermore, the DHFR V resistance mechanism, previously identified in strains of Shigella sonnei isolated in Sicily and associated with travellers from Sri Lanka, has not yet appeared in salmonellas in Sicily.
Insights
Trimethoprim resistance in Salmonella strains from Sicily was investigated. The common DHFR I resistance mechanism was rare, and DHFR V was absent in these Salmonella, unlike other bacteria.
Area of Science:
- Microbiology
- Antimicrobial Resistance
- Molecular Biology
Background:
- Trimethoprim (Tp) resistance is a growing concern in bacterial pathogens.
- Salmonella species are significant human and animal pathogens.
- Understanding resistance mechanisms is crucial for effective treatment and control.
Purpose of the Study:
- To investigate the occurrence and mechanisms of trimethoprim resistance in Salmonella isolates from Sicily.
- To characterize the specific dihydrofolate reductase (DHFR) gene types involved in trimethoprim resistance.
Main Methods:
- Bacterial isolation and identification from human and water samples.
- Antimicrobial susceptibility testing for trimethoprim and sulphonamides.
- Plasmid DNA analysis and characterization.
- Hybridization assays using probes for DHFR gene types I, II, IV, and V.
Main Results:
- 23 out of 765 Salmonella strains (3%) exhibited high-level trimethoprim resistance.
- Resistance was often plasmid-encoded and frequently associated with sulphonamide resistance.
- DHFR type I was detected in a small number of strains, while DHFR types II, IV, and V were not detected.
- Six Salmonella serovars harbored trimethoprim-resistant strains, with Salmonella typhimurium being the most prevalent.
Conclusions:
- The DHFR type I resistance mechanism is uncommon in Sicilian Salmonella isolates compared to other European enterobacteria.
- The DHFR V resistance mechanism, seen in Shigella sonnei, has not yet emerged in Salmonella in Sicily.
- Plasmid-mediated trimethoprim resistance in Salmonella presents a public health challenge requiring ongoing surveillance.