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Published on: July 22, 2011
Antimicrobial resistance pattern and plasmid profile of Salmonella typhi isolated from an outbreak in Tehran province
1Molecular Microbiology Unit, Pasteur Institute of Iran, Tehran, Islamic Republic of Iran.
Abstract:
The antimicrobial resistance patterns and plasmid profiles of Salmonella typhi isolates from sporadic cases (n = 33) and an outbreak (n = 48) were compared. Of 28 sporadic drug-resistant isolates, 24 (85.7%) were multiply resistant. The predominant antibiotic resistance pattern was TeCmSmSxTAp, which was also the most common pattern of the outbreak isolates. 13 drug-resistant strains isolated before the outbreak (46.4%) were able to transfer the whole resistance pattern or part of it to Escherichia coli K 12 by conjugation. Although 20 of the sporadic strains contained plasmid DNA, transferable R plasmids were only detected in 13 (65%) of them. Among the outbreak strains, the rate of R plasmid transfer was 92.3%, with only the TeCmSmSxTAp pattern transferred. Plasmid profiling and Hind III endonuclease digestion of plasmid DNA identified a 91.2 megadaltons (Mda) plasmid that was recovered from most of the outbreak isolates and from 4 strains collected before the outbreak. This plasmid coded for TeCmSmSxtAp and transferred the pattern of resistance in toto. The results indicate multidrug-resistant S. typhi as a potential cause of infection in the region.
Insights
Multidrug-resistant Salmonella typhi strains exhibit concerning antimicrobial resistance patterns. A specific 91.2 Mda plasmid carrying resistance genes was identified in both sporadic and outbreak isolates, facilitating resistance transfer.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- Antimicrobial resistance (AMR) in Salmonella typhi poses a significant public health threat.
- Understanding resistance mechanisms and plasmid profiles is crucial for controlling typhoid fever.
Purpose of the Study:
- To compare antimicrobial resistance patterns and plasmid profiles of Salmonella typhi from sporadic cases and an outbreak.
- To identify the genetic elements responsible for multidrug resistance in S. typhi.
Main Methods:
- Antimicrobial susceptibility testing was performed on S. typhi isolates.
- Plasmid DNA was extracted, analyzed by profiling, and digested with Hind III endonuclease.
- Conjugation experiments were conducted to assess R plasmid transfer to Escherichia coli K 12.
Main Results:
- A predominant multidrug resistance pattern (TeCmSmSxTAp) was observed in both sporadic and outbreak isolates.
- Transferable R plasmids were detected in 65% of sporadic and 92.3% of outbreak strains.
- A 91.2 Mda plasmid carrying the TeCmSmSxtAp resistance pattern was identified and found to be transferable.
Conclusions:
- Multidrug-resistant S. typhi, particularly strains harboring the 91.2 Mda plasmid, are a significant cause of infection in the region.
- The transferability of resistance genes via plasmids highlights the potential for rapid dissemination of antimicrobial resistance.
- Effective surveillance and control strategies are needed to combat the spread of resistant S. typhi strains.
