Salmonella

Salmonella is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of Salmonella are Salmonella enterica and Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes. Salmonella was named after Daniel Elmer Salmon (1850–1914), an American veterinary surgeon. Salmonella species are non-spore-forming, predominantly motile enterobacteria with cell diameters between about 0.7 and 1.5 µm, lengths from 2 to 5 µm, and peritrichous flagella (all around the cell body). They are chemotrophs, obtaining their energy from oxidation and reduction reactions using organic sources. They are also facultative aerobes, capable of generating ATP with oxygen ('aerobically') when it is available, or when oxygen is not available, using other electron acceptors or fermentation ('anaerobically'). S. enterica subspecies are found worldwide in all warm-blooded animals and in the environment. S. bongori is restricted to cold-blooded animals, particularly reptiles. Salmonella species are intracellular pathogens; certain serotypes causing illness. Nontyphoidal serotypes can be transferred from animal-to-human and from human-to-human. They usually invade only the gastrointestinal tract and cause salmonellosis, the symptoms of which can be resolved without antibiotics. However, in sub-Saharan Africa, nontyphoidal Salmonella can be invasive and cause paratyphoid fever, which requires immediate treatment with antibiotics. Typhoidal serotypes can only be transferred from human-to-human, and can cause food-borne infection, typhoid fever, and paratyphoid fever. Typhoid fever is caused by Salmonella invading the bloodstream (the typhoidal form), or in addition spreads throughout the body, invades organs, and secretes endotoxins (the septic form). This can lead to life-threatening hypovolemic shock and septic shock, and requires intensive care including antibiotics. The collapse of the Aztec society in Mesoamerica is linked to a catastrophic Salmonella outbreak, one of humanity's deadliest, that occurred after the Spanish conquest. The genus Salmonella is part of the family of Enterobacteriaceae. Its taxonomy has been revised and has the potential to confuse. The genus comprises two species, S. bongori and S. enterica, the latter of which is divided into six subspecies: S. e. enterica, S. e. salamae, S. e. arizonae, S. e. diarizonae, S. e. houtenae, and S. e. indica. The taxonomic group contains more than 2500 serotypes (also serovars) defined on the basis of the somatic O (lipopolysaccharide) and flagellar H antigens (the Kauffman–White classification). The full name of a serotype is given as, for example, Salmonella enterica subsp. enterica serotype Typhimurium, but can be abbreviated to Salmonella Typhimurium. Further differentiation of strains to assist clinical and epidemiological investigation may be achieved by antibiotic sensitivity testing and by other molecular biology techniques such as pulsed-field gel electrophoresis, multilocus sequence typing, and, increasingly, whole genome sequencing. Historically, salmonellae have been clinically categorized as invasive (typhoidal) or noninvasive (nontyphoidal salmonellae) based on host preference and disease manifestations in humans. Salmonella was first visualized in 1880 by Karl Eberth in the Peyer's patches and spleens of typhoid patients. Four years later, Georg Theodor Gaffky was able to successfully grow the pathogen in pure culture. A year after that, medical research scientist Theobald Smith discovered what would be later known as Salmonella enterica (var. Choleraesuis). At the time, Smith was working as a research laboratory assistant in the Veterinary Division of the United States Department of Agriculture. The department was under the administration of Daniel Elmer Salmon, a veterinary pathologist. Initially, Salmonella Choleraesuis was thought to be the causative agent of hog cholera, so Salmon and Smith named it 'Hog-cholerabacillus'. The name Salmonella was not used until 1900, when Joseph Leon Lignières proposed that the pathogen discovered by Salmon's group be called Salmonella in his honor.:16 Serotyping is done by mixing cells with antibodies for a particular antigen. It can give some idea about risk. For example, in 2014, a study showed that S. Reading is very common among young turkey samples, but it is not a significant contributor to human salmonellosis. Serotyping can assist identify the source of contamination. For example, if we have a case of food illness. There are two ways to figure out the source of contamination. One of them is serotyping the Salmonella in infected people, and serotyping Salmonella found at possible source of contamination (e.g. where food was prepared), and then determining if the serotypes match. The other way is to serotype the Salmonella in infected people, see the result and if the result matches with a particular kind of serotype of Salmonella that can only found in a particular species of animals or at particular place, then we can know our source of contamination.  Moreover, serotyping may suggest adequate treatment by giving us the idea about the antibiotic resistance of salmonella species. For example, sulfonamides are antibiotics which are appropriate for treatment of Salmonella enterica serotype Typhi (normally it is just shortened to S.Typhi). Serotyping is a faster method than antibiotic sensitivity testing culture methods. Most subspecies of Salmonella produce hydrogen sulfide, which can readily be detected by growing them on media containing ferrous sulfate, such as is used in the triple sugar iron test. Most isolates exist in two phases, a motile phase I and a nonmotile phase II. Cultures that are nonmotile upon primary culture may be switched to the motile phase using a Craigie tube or ditch plate. RVS broth can be used to enrich for Salmonella species for detection in a clinical sample.