ABSTRACTSalmonella entericaserovar Typhimurium is one of approximately 2,500 distinct serovars of the genusSalmonellabut is exceptional in its wide distribution in the environment, livestock, and wild animals.S. Typhimurium causes a large proportion of nontyphoidalSalmonella(NTS) infections, accounting for a quarter of infections, second only toS. entericaserovar Enteritidis in incidence.S. Typhimurium was once considered the archetypal broad-host-rangeSalmonellaserovar due to its wide distribution in livestock and wild animals, and much of what we know of the interaction ofSalmonellawith the host comes from research using a small number of laboratory strains of the serovar (LT2, SL1344, and ATCC 14028). But it has become clear that these strains do not reflect the genotypic or phenotypic diversity ofS. Typhimurium. Here, we review the epidemiological record ofS. Typhimurium and studies of the host-pathogen interactions of diverse strains ofS. Typhimurium. We present the concept of distinct pathovariants ofS. Typhimurium that exhibit diversity of host range, distribution in the environment, pathogenicity, and risk to food safety. We review recent evidence from whole-genome sequencing that has revealed the extent of genomic diversity ofS. Typhimurium pathovariants, the genomic basis of differences in the level of risk to human and animal health, and the molecular epidemiology of prominent strains. An improved understanding of the impact of genome variation of bacterial pathogens on pathogen-host and pathogen-environment interactions has the potential to improve quantitative risk assessment and reveal how new pathogens evolve.
Molecular epidemiology: The impact of molecular biology in epidemiology research