Comparative Genome Analysis of the High Pathogenicity <em>Salmonella</em> Typhimurium Strain UK-1

Salmonella enterica serovar Typhimurium, a gram-negativefacultative rod-shaped bacterium causing salmonellosis and foodborne disease,is one of the most common isolated Salmonella serovars inboth developed and developing nations. Several S. Typhimuriumgenomes have been completed and many more genome-sequencing projects are underway.Comparative genome analysis of the multiple strains leads to a better understandingof the evolution of S. Typhimurium and its pathogenesis. S.Typhimurium strain UK-1 (belongs to phage type 1) is highly virulent whenorally administered to mice and chickens and efficiently colonizes lymphoidtissues of these species. These characteristics make this strain a good choicefor use in vaccine development. In fact, UK-1 has been used as the parentstrain for a number of nonrecombinant and recombinant vaccine strains, includingseveral commercial vaccines for poultry. In this study, we conducted a thoroughcomparative genome analysis of the UK-1 strain with other S.Typhimurium strains and examined the phenotypic impact of several genomicdifferences. Whole genomic comparison highlights an extremely close relationshipbetween the UK-1 strain and other S. Typhimurium strains;however, many interesting genetic and genomic variations specific to UK-1were explored. In particular, the deletion of a UK-1-specific gene that ishighly similar to the gene encoding the T3SS effector protein NleC exhibiteda significant decrease in oral virulence in BALB/c mice. The complete geneticcomplements in UK-1, especially those elements that contribute to virulenceor aid in determining the diversity within bacterial species, provide keyinformation in evaluating the functional characterization of important geneticdeterminants and for development of vaccines.