Salmonella are a group of closely related rod-shaped, Gram-stained negative bacteria that have flagella (tail-like structures used for movement). Salmonella types are further characterized by specific proteins found on the bacterial and flagellar surface. Each different combination of protein coats is termed a serovar. Serovars are distinguished usually by special laboratories with immunologic tests.
The nomenclature of specific types of Salmonella has changed in recent decades. Currently, many investigators consider the over 2,500 serovars to be members of only two species, S. enterica or S. bongori. However, many serovars were considered to be and named as individual species in the past before more sophisticated genetic methods to characterize separate species were available. Consequently, many of the old serovar names are still seen in the medical literature, such as S. enteritidis, S. typhimurium, S. typhi, S. newport, and S. choleraesuis. In other cases, doctors simply avoid the name problem and identify all isolates as Salmonella spp (species) since the bacteria of this group are so closely related.
Salmonella infections cause diseases in humans (for example, salmonellosis, gastroenteritis, typhoid fever, and paratyphoid fever), animals, and birds. They are one of the major causes of gastroenteritis in both industrialized and third-world countries and are considered to be the most common cause of food-borne disease in the U.S. Salmonella were first isolated from infected pigs in 1885 by Theobald Smith and were named after his lab director, D.E. Salmon.
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