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Molecular fingerprinting of multidrug-resistant Salmonella enterica serotype Typhi
M D Hampton1, L R Ward, B Rowe
1Central Public Health Laboratory, London, United Kingdom.
Abstract:
For epidemiologic investigations, the primary subdivision of Salmonella Typhi is vi-phage typing; 106 Vi-phage types are defined. For multidrug-resistant strains the most common types have been M1 (Pakistan) and E1 (India, Pakistan, Bangladesh, and the Arabian Gulf); a strain untypable with the Vi phages has been responsible for a major epidemic in Tajikistan. Most often, isolates from the Indian subcontinent have been resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, tetracyclines, and trimethoprim; but in the 1997 Tajikistan outbreak, the epidemic strain was also resistant to ciprofloxacin. For multidrug-resistant strains, subdivision within phage type can be achieved by plasmid profile typing and pulsed-field gel electrophoresis.
Insights
Salmonella Typhi strains are classified by Vi-phage typing, with common multidrug-resistant types M1 and E1. A novel strain resistant to ciprofloxacin caused a major epidemic in Tajikistan.
Area of Science:
- Microbiology
- Epidemiology
- Infectious Diseases
Background:
- Salmonella Typhi is a significant human pathogen responsible for typhoid fever.
- Vi-phage typing is the primary method for subdividing Salmonella Typhi strains in epidemiological studies.
- Multidrug-resistant (MDR) strains pose a substantial public health challenge.
Purpose of the Study:
- To describe the predominant Vi-phage types of Salmonella Typhi, particularly MDR strains.
- To highlight the emergence of novel MDR Salmonella Typhi strains with reduced susceptibility to antibiotics.
- To discuss advanced subtyping methods for MDR strains.
Main Methods:
- Vi-phage typing for Salmonella Typhi strain classification.
- Analysis of antimicrobial resistance patterns, including resistance to ciprofloxacin.
- Plasmid profile typing and pulsed-field gel electrophoresis for subtyping MDR strains.
Main Results:
- 106 distinct Vi-phage types of Salmonella Typhi have been defined.
- M1 (Pakistan) and E1 (India, Pakistan, Bangladesh, Arabian Gulf) are common MDR types.
- A Vi-phage untypable strain resistant to ciprofloxacin caused a major epidemic in Tajikistan.
Conclusions:
- Vi-phage typing is crucial for tracking Salmonella Typhi epidemiology.
- The emergence of ciprofloxacin-resistant strains is a serious concern.
- Plasmid profiling and PFGE are valuable tools for characterizing MDR Salmonella Typhi.