Salmonella Typhimurium DT104: An Emerging Salmonella in Livestock and Humans

In the past four years there has been an increase in the reported prevalence of salmonellosis in dairy cattle in the Pacific Northwest. We have established that Salmonella typhimurium DT104 is responsible for much of this increase. S. typhimurium DT104 is emerging as a pathogen in the Pacific Northwest and elsewhere in the United States and has importance for animal and human health. S. typhimurium DT104 is a specific epidemic strain. Salmonella spp are initially categorized by biochemical, somatic and flagellar antigen characteristics which allows them to be placed into named serovars. Most reports of salmonellosis in animals define isolates to this level. Epidemiological studies require a more finite identification within serovars. Traditionally, phage susceptibility has been used with S. typhimurium isolated from cattle combined with further categorization of biotype, antibiotic sensitivity and by the determination of differences in genetic constituents especially plasmid profiles. The designation DT104 (determinant type 104) is established by phage susceptibility coupled with further categorizion by plasmid content and by antibiogram. The epidemic strain has an antibiotic resistance pattern characterized by resistance to ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracycline (R-type ACSSuT) and a plasmid profile char-