Comparative Genomics of Salmonella enterica Serovar Typhi Strains

We present the 4.8-Mb complete genome sequence of Salmonella enterica serovar Typhi strain Ty2, a human-specific pathogen causing typhoid fever. A comparison with the genome sequence of recently isolated S. enterica serovar Typhi strain CT18 showed that 29 of the 4,646 predicted genes in Ty2 are unique to this strain, while 84 genes are unique to CT18. Both genomes contain more than 200 pseudogenes; 9 of these genes in CT18 are intact in Ty2, while 11 intact CT18 genes are pseudogenes in Ty2. A half-genome interreplichore inversion in Ty2 relative to CT18 was confirmed. The two strains exhibit differences in prophages, insertion sequences, and island structures. While CT18 carries two plasmids, one conferring multiple drug resistance, Ty2 has no plasmids and is sensitive to antibiotics. Salmonella enterica serovar Typhi is a human-specific patho-gen causing enteric typhoid fever, a severe infection of the reticuloendothelial system (8, 10, 14). Although difficult to estimate, it is thought that at least 16 million cases and 500,000 deaths occur each year around the world (8). The early admin-istration of antibiotic treatment has proven to be highly effec-tive in eliminating infections, but indiscriminate use of antibi