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*{+}Background:+* Salmonella enterica subsp. enterica serovar Typhi (antigenic formula 9,12\[Vi\]:d:--) is a serovar of the O:9 (D1) serogroup. S. Typhi causes typhoid fever, a life-threatening disease characterized by sustained fever as high as 103° to 104° F (39° to 40° C). In developed countries, this serovar is considered rare; however, in developing countries in Africa, Asia, and Latin America is among the top ten Salmonella serovars causing disease in humans, where it kills approx. 600.000 people annually. A number of projects have sequenced the genome of S. Typhi strains; these studies have concluded that S. Typhi is a highly clonal serovar that emerged approx. 30,000--50,000 years ago. Horizontal gene transfer had played an important role in the evolution S. Typhi, including the acquisition of plasmids encoding multiple antibiotic resistant genes.