Salmonella
Salmonella are enteric bacteria of the genus Salmonella, named in honor of the American veterinarian Daniel Elmer Salmon even if the man who discovered the genre was Theobald Smith, who worked under the direction of Salmon to the Bureau of Animal Industry (BAI ) 1884.
Taxonomy
According to the recent work of taxonomy, in particular by DNA hybridization, the genus Salmonella comprises two species, the main (long considered the only one), Salmonella enterica consists of over 2000 serotypes or subspecies - which The most common is Salmonella enterica Enterica - themselves divided into numerous serovars (Enteritidis, Derby, Hadar, Infantis, Paratyphi, Typhi, Typhimurium, Virchow, etc..).
Salmonella species are the following:
* Salmonella bongori;
* Salmonella enterica;
* Salmonella enterica arizonae;
* Salmonella enterica Diarizonae;
* Salmonella enterica Enterica;
* Salmonella enterica houtenae;
* Salmonella enterica indica;
* Salmonella enterica Salamae;
* Salmonella subterranea (since 2004).
In 2000, the National Reference Centre for Salmonella and Shigella (CNRSS) of the Institute Pasteur in Paris, had listed 883 Salmonella strains of human origin. Serovars Enteritidis and Typhimurium accounted for 36% and 29%. We know today more than 2000 serotypes of salmonella.
Biochemical characters
They are Gram-negative enterobacteria, mobile (peritrichous cilia), aero-facultative anaerobes, oxidase - Nitrate reductase + fermentation of glucose, lactose -, H2S + (or -), urease -, lysine decarboxylase +, using lane mixed acid, indole-, not having the beta-galactosidase, high infectivity, responsible for gastroenteritis, food poisoning and typhoid fever and paratyphoid (S. typhi and S. paratyphi).
Infectious dose
There is no standard infectious dose, which depends:
1. the pathogenicity of the strain (or serovar) considered
2. factors of host susceptibility
3. microbial concentration (dose in contact or ingestion).
Antigenic characters
Like all Enterobacteriaceae, Salmonella somatic O antigens have (located in the wall). There are 67 different O-antigen is a major characteristic of a group of Salmonella O-antigen is a minor accessory. The deletion mutation of the O-antigen leads to partial or complete loss of pathogenicity.
Salmonella flagellar antigens have also H. They are present in two different forms (phase). In both of these forms (biphasic) or in the form of a single phase (monophasic). These two phases are encoded by two different genes, but very similar, they must originate from the duplication of a single ancestral gene.
Finally, Salmonella ser. Typhi, S. ser. Paratyphi C and S. ser. Dublin possess the capsular antigen Vi polysaccharide nature can (more or less) hide the somatic O. The latter is unmasked by the destruction of Vi antigen (heating at 100 ° C for 10 min).
Habitat
Salmonella can survive several weeks in dry and several months in water. They occur so frequently in aquatic environments polluted, contaminated by feces of carrier animals is very important. Aquatic vertebrates, including birds (Anatidae) and reptiles (Chelonia) are important vectors of salmonella. Poultry, cattle and sheep are animals frequently contaminant, Salmonella may be found in foods, including meat and raw eggs.
Syndromes typhoid and paratyphoid
Four serotypes of Salmonella have adapted to humans, which is the only reservoir and in whom they cause a specific disease. These S. typhi (typhoid bacillus), S. paratyphi A, S. paratyphi B (bacillus Schotmüller) and S. paratyphi C (bacillus Hirschfeld), incidentally S. sendai. The germs enter, even in small numbers, through ingestion and after a fairly long incubation (up to 3 weeks) cross the intestinal mucosa and invade the lymphoid tissue pre-intestinal (Peyer). From there, the germ passes with the lymph into the circulation, which determines a state sepsis. Sepsis is a complication not accidental but part of the normal evolution of the disease. In addition, Peyer's patches may ulcerate and cause intestinal perforation and peritonitis. The patient recovered carrier of germs can remain for months or years, especially persistent bacteria in the bile ducts.
The release of endotoxin plays an important role in the pathogenesis of the disease, hence the danger of administering a high dose of antibiotic that may cause mass lysis of bacteria.
Transmission occurs primarily through drinking water during epidemics spread. But direct contact or food may also be implicated in the spread. The strict bacteriological control of drinking water and monitoring the reservoir of germs (carriers) account for the dramatic reduction of typhoid and paratyphoid in countries with developed health.
Food poisoning or salmonella enteritis
Responsible group consisting of potentially all other serotypes (over a thousand), most of which have never yet been found in humans. These are encountered in various Salmonella species, most having never been linked to a specific host and can also infect humans. It is therefore a zoonosis.
The organism enters through the digestive tract and must be ingested in large numbers to cause disease in healthy adults. The gastric acidity was also in charge of the destruction of the majority of ingested bacteria. The contagion is carried by massive ingestion of foods in which the germ has swarmed like in a culture medium.
However, infants and young children are more susceptible to infection which can be achieved by ingesting a small number of bacteria. It has been shown that, in infants, the contamination could be through inhalation of bacteria-laden dust. After a short incubation period of a few hours one day, the germ multiplies in the intestinal lumen causing an intestinal inflammation with diarrhea often muco-purulent and bloody. In infants, dehydration can cause a state of severe toxicosis. The disease usually is mild. There is normally no sepsis, but it can occur exceptionally as a complication in patients debilitated (Hodgkin's disease, eg.). Extraintestinal localizations are possible, especially salmonella meningitis in children, osteitis, etc....
Epidemiology of foodborne illness
Epidemiology involves food, especially meat, eggs and dairy products.
These have a high salmonella outbreak in the summer. The majority of salmonella enteritis occur in young children, in the form of scattered cases. At least 25% of summer enteritis in young children are caused by salmonella. In Western Europe, S. typhimurium represents nearly 70% of isolates!
See also Escherichia coli
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