Salmonella enterica

Salmonella enterica is a rod shaped, flagellated, Gram-negative bacterium, and a member of the genus Salmonella.

Serovars
S. enterica has an extraordinarily large number of serovars or strains&mdash;up 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.

Salmonella Typhi
Salmonella Typhi is a serovar of Salmonella enterica (formerly known as Salmonella choleraesuis) and the cause of the disease typhoid fever. The organism can be transmitted by the fecal-oral route&mdash;it is excreted by humans in feces and may be transmitted by contaminated water, food, or by person-to-person contact (with inadequate attention to personal hygiene).

Salmonella Typhi possesses three main antigenic factors: the O, or somatic antigen; the Vi, or encapsulation antigen; and the H, or flagellar antigen.

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