Salmonella enterica serovar Typhimurium T000240

Salmonella enterica serovar Typhimurium is one of the most important causative agents of acute human Salmonella gastroenteritis. The emergence of multidrug-resistant strains of S. enterica serovar Typhimurium have been reported in various countries, raising concerns about the difficulty in the treatment of infections. S. enterica serovar Typhimurium T000240 was isolated from a human source in 2000 as the first isolated strain displaying a high-level fluoroquinolone resistance in Japan.

The complete genome of S. enterica serovar Typhimurium T000240 consisted of a chromosome (4,954,814 bp; G+C content 52.2 %) and two circular plasmids (pSTMDT12_L: 106,510 bp; and pSTMDT12_S: 8,670 bp). An 82-kb genomic island, designated as GI-DT12, related to its highly resistant phenotype was identified on the chromosome. As GI-DT12 was revealed to be flanked by IS1-derivatives, IS1-mediated recombination likely played a role in the acquisition of this genomic island through horizontal transfer. Furthermore, the gene cassette responsible for gentamicin and trimethoprim resistance was identified on plasmid pSTMDT12_L, and appeared to have been acquired through homologous recombination with IS26.) Such ISs may represent potential landmarks to obtain variety of genetic elements present on the plasmids and chromosomes of pathogenic bacteria.