Salmonella enterica

# Overview
Salmonella enterica is a rod shaped, flagellated, Gram-negative bacterium, and a member of the genus Salmonella. S. enterica has an extraordinarily large number of serovars or strainsup to 2000 have been described. Salmonella Typhi is a serovar of Salmonella enterica and the cause of the disease typhoid fever.

# Serovars
- S. enterica has an extraordinarily large number of serovars or strainsup to 2000 have been described.
- Salmonella enterica Serovar Typhi (historically elevated to species status as S. typhi) is the disease agent in typhoid fever.
- Other serovars such as Typhimurium (also known as S. typhimurium) can lead to a form of human gastroenteritis sometimes referred to as salmonellosis.
- The genome sequences of serovars Typhi and Typhimurium LT2 have been established. Also an analysis of the proteome of Typhimurium LT2 under differing environmental conditions has been performed 
- Other Salmonellae which may cause symptoms similar to typhoid fever include:
- Salmonella Paratyphi A
- Salmonella Paratyphi B
- Salmonella Paratyphi C
- Salmonella choleraesuis

## Salmonella Typhi
Salmonella Typhi is a serovar of Salmonella enterica and the cause of the disease typhoid fever.
Features of Salmonella Typhi
- Gram negative bacillus
- Flagellated
- Facultatively anaerobic
- Three antigens O,H and Vi
- O polysaccharide antigen
- H flagellar antigen
- Vi outer capsular polysaccharide antigen
- Belongs to Enterobacteriaceae family
- Chemotroph
Transmission of Salmonella typhi
- Fecal-oral route
- Excretion in human feces causing transmission by contaminated water, food, or by person-to-person contact.

# Epidemiology
Most cases of salmonellosis are caused by food infected with S. enterica, which often infects cattle and poultry, though also other animals such as domestic cats and hamsters have also been shown to be sources of infection to humans.  However, investigations of vacuum cleaner bags have shown that households can act as a reservoir of the bacterium; this is more likely if the household has contact with an infection source, for example through members working with cattle or in a veterinary clinic.
Raw chicken and goose eggs can harbor salmonella enterica, initially in the whites of the eggs, although most eggs are not infected. As the egg ages at room temperature, the yolk membrane begins to break down and salmonella enterica can spread into the yolk. Refrigeration and freezing do not kill all the bacteria, but substantially slow or halt their growth. Pasteurizing (briefly heating to a specific temperature) and irradiation are used to kill salmonella for commercially produced foodstuffs containing raw eggs such as ice cream. Foods prepared in the home from raw eggs such as mayonnaises, cakes and cookies can spread salmonella if not properly cooked before consumption. See Egg (food).

# Space bacteria
On September 25, 2007, Cheryl Nickerson (Center for Infectious Diseases and Vaccinology) at Arizona State University stated that space bacteria Salmonella typhimurium (food bugs, on their 12-day Atlantis orbiter flight, September 2006) were found to change the way they expressed 167 genes (regulated by a protein Hfq). It gained 3 times virulence than on earth.

# Also see
- Typhoid Mary

# Gallery
- Gram-negative Salmonella typhimurium bacteria that had been isolated from a pure culture (8000x mag). From Public Health Image Library (PHIL). 
- Gram-negative Salmonella typhimurium bacteria that had been isolated from a pure culture (20000X mag). From Public Health Image Library (PHIL). 
- Gram-negative Salmonella typhimurium bacteria that had been isolated from a pure culture (25000X mag). From Public Health Image Library (PHIL).