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Characterization of multi-drug resistant Salmonella typhi isolated from Pakistan
P M Shanahan1, K A Karamat, C J Thomson
1Department of Medical Microbiology, University of Edinburgh, UK.
Abstract:
Thirty-nine strains of Salmonella typhi, isolated in 1995 from four Districts in Pakistan, Rawalpindi, Islamabad, Kharian and Jehlem, were catalogued and examined. Chromosomal DNA from each isolate was digested with XbaI restriction endonuclease and subjected to pulsed-field gel electrophoresis. Three clonal variants comprising of 17-19 DNA fragments were identified. Antibiotic susceptibility testing identified that 37 of the S. typhi were resistant to chloramphenicol, trimethoprim and ampicillin. These antibiotic resistance genes were found to be located on one of four plasmids belonging to incompatibility group IncHI1 and ranging in size from 150-175 Kb. The genes responsible for this resistance in each case were the chloramphenicol acetyltransferase (CAT) type I, the dihydrofolate reductase (DHFR) type VII and the beta-lactamase TEM-1 respectively.
Insights
This study examined Salmonella typhi strains from Pakistan, revealing three main variants. Most strains showed resistance to common antibiotics like chloramphenicol, trimethoprim, and ampicillin, linked to specific resistance genes on plasmids.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Salmonella typhi is a significant cause of typhoid fever globally.
- Antibiotic resistance in S. typhi poses a major public health challenge.
- Understanding the genetic basis of resistance is crucial for effective treatment and control.
Purpose of the Study:
- To characterize Salmonella typhi isolates from Pakistan.
- To identify clonal variants and their antibiotic resistance profiles.
- To determine the genetic location of antibiotic resistance genes.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) of XbaI-digested chromosomal DNA.
- Antibiotic susceptibility testing.
- Plasmid analysis to identify resistance gene location.
Main Results:
- Thirty-nine S. typhi strains from Pakistan were analyzed.
- Three distinct clonal variants were identified using PFGE.
- 37 out of 39 isolates were resistant to chloramphenicol, trimethoprim, and ampicillin.
- Resistance genes (CAT I, DHFR VII, TEM-1) were located on IncHI1 plasmids (150-175 Kb).
Conclusions:
- The study identified prevalent clonal variants of S. typhi in Pakistan.
- Widespread multidrug resistance in S. typhi is associated with specific plasmid-borne genes.
- These findings highlight the need for enhanced surveillance and antimicrobial stewardship.