Genetic dynamics and molecular epidemiology of Salmonella typhi

A large number of S. typhi isolates from various geographic regions, representing sporadic, outbreak and environmental isolates, as well as isolates from fatal and non-fatal cases of typhoid fever have been analysed by pulsed-field gel electrophoresis (PFGE) with the restriction endonucleases XbaI, SpeI, AvrII, and ICeuI. The main conclusions are: (1) significant genetic diversity exists among these isolates; (2) outbreak isolates are more homogeneous compared to sporadic isolates; (3) there is movement of certain PFGE types among the countries of Southeast Asia; (4) environmental isolates also show diversity and share PFGE types with clinical strains; there appear to be a correlation between PFGE pattern and isolates from fatal disease; (6) limited diversity exists in a region where typhoid fever is a recent introduction; (7) there is significant diversity in total genome size; (8) genomic rearrangements within the rrn operon has occurred among many of these strains. Our findings emphasize the genomic plasticity of S. typhi and it is likely that this is closely related to the pathogenic potential and virulence of this organism.