- 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.
Symptoms of Salmonella Infection
The symptoms of Salmonella infections depend on the overall health of the infected person (for example, normal or with a suppressed immune system) and the particular serovar infecting the patient. Symptoms usually begin about 12-72 hours after ingestion of the bacteria. In general, people contract S. spp (for example, serovars S. enteritidis, S. cholerasuis) that usually cause a self-limiting diarrhea, nausea, and vomiting termed salmonellosis or S. gastroenteritis. Fever may be present but usually lasts only one to three days, with all the symptoms resolving in about three to seven days. This gastroenteritis is not always traced to the bacterial source and is sometimes simply termed "food poisoning," a term used to describe similar symptoms caused by several different bacterial, parasitic, and viral organisms (for example, E. coli Giardia, and rotavirus). Those with a suppressed immune system, the elderly, and neonates may develop more severe symptoms (for example, bacteremia or sepsis).
Fever and the above-mentioned symptoms lasting over seven to 10 days suggest infection with the more virulent serovars, S. typhi or S. paratyphi. S. typhi causes typhoid fever, which includes symptoms of a high fever (104 F), abdominal pains, sweating, and confusion; some of those affected may develop swollen lymph nodes. About half of patients develop a slow heartbeat (bradycardia), and some get slightly raised red or rose-colored spots (rose spots) on the chest and abdomen. S. paratyphi causes paratyphoid fever, a disease similar to but with less severe symptoms than typhoid fever. Some untreated patients who become infected with S. typhi or S. paratyphi and are otherwise healthy will resolve the infection in about one month, but others can suffer complications (for example, becoming a carrier of the organism, developing organ infections, sepsis, and potentially death).
Medically Reviewed by a Doctor on 5/25/2016
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