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Food-Info.net> Topics > Food Safety > Bacteria > Overview of food-borne bacteria

Salmonella spp

General characteristics

Salmonella is the name of a genus of a rod-shaped, motile bacteria (nonmotile exceptions are S. gallinarum and S. pullorum ), nonsporeforming and Gram-negative. There is a widespread occurrence in animals, especially in poultry and swine. Environmental sources of the organism include water, soil, insects, factory surfaces, kitchen surfaces, animal faeces, raw meats, raw poultry, and raw seafoods, to name only a few.


Source

Disease symptoms

S. typhi and the paratyphoid bacteria are normally caused septicemic and produce typhoid or typhoid-like fever in humans. Other forms of salmonellosis generally produce milder symptoms.

Acute symptoms -- Nausea, vomiting, abdominal cramps, diarrhoea, fever, and headache. Chronic consequences -- arthritic symptoms may follow 3-4 weeks after onset of acute symptoms.

Onset time -- 6-48 hours.

Infective dose -- As few as 15-20 cells; depends upon age and health of host, and strain differences among the members of the genus.

Duration of symptoms -- Acute symptoms may last for 1 to 2 days or may be prolonged, again depending on host factors, ingested dose, and strain characteristics.

Cause of disease -- Penetration and passage of Salmonella organisms from gut lumen into epithelium of small intestine where inflammation occurs; there is evidence that an enterotoxin may be produced, perhaps within the enterocyte.

Diagnosis

Serological identification of culture isolated from stool.

Associated foods

Raw meats, poultry, eggs, milk and dairy products, fish, shrimp, frog legs, yeast, coconut, sauces and salad dressing, cake mixes, cream-filled desserts and toppings, dried gelatin, peanut butter, cocoa, and chocolate.

Various Salmonella species have long been isolated from the outside of egg shells. The present situation with S. enteritidis is complicated by the presence of the organism inside the egg, in the yolk. This and other information strongly suggest vertical transmission, i.e., deposition of the organism in the yolk by an infected layer hen prior to shell deposition. Foods other than eggs have also caused outbreaks of S. enteritidis disease.

Prevention

Salmonella is heat-sensitive and will be killed by thorough heating (over 70 °C). Raw or undercooked foods and cross-contamination, when cooked material comes into contact with raw produce or contaminated materials (cutting boards), are the main causes of infection. Proper cooking and hygienic food handling thus can prevent Salmonella infections to a large extend.

Complications

S. typhi and S. paratyphi A, B, and C produce typhoid and typhoid-like fever in humans. Various organs may be infected, leading to lesions. The fatality rate of typhoid fever is 10% compared to less than 1% for most forms of salmonellosis. S. dublin has a 15% mortality rate when septicemic in the elderly, and S. enteritidis is demonstrating approximately a 3.6% mortality rate in hospital/nursing home outbreaks, with the elderly being particularly affected.

Salmonella septicemia has been associated with subsequent infection of virtually every organ system.

Postenteritis reactive arthritis and Reiter's syndrome have also been reported to occur generally after 3 weeks. Reactive arthritis may occur with a frequency of about 2% of culture-proven cases. Septic arthritis, subsequent or coincident with septicemia, also occurs and can be difficult to treat.

Risk populations

All age groups are susceptible, but symptoms are most severe in the elderly, infants, and the infirm. AIDS patients suffer salmonellosis frequently (estimated 20-fold more than general population) and suffer from recurrent episodes.

Sources:

The bad bug book : http://www.cfsan.fda.gov/~mow/intro.html

 



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