Salmonella spp.

Salmonella species are rod-shaped, Gram-negative bacteria. They cause food poisoning (salmonellosis), and one type, S. typhi, causes typhoid fever.Transmission. Salmonella lives in the intestines of many animals, especially poultry. People are infected by eating food or drinking water contaminated with it, for example undercooked chicken or eggs, or food handled after touching raw meat. It is spread by the faecal-oral route when hygiene is poor.How it causes disease. Some bacteria survive the acid in the stomach and reach the small intestine. They attach to the epithelial cells lining the gut and cause these cells to take them in, so the bacteria invade and multiply inside the gut lining. Their endotoxins (lipopolysaccharide in the outer membrane) trigger an inflammatory response in the gut wall. This damages the epithelium and causes fluid to be lost into the gut.Symptoms appear about 12 to 72 hours after infection: diarrhoea, abdominal cramps, vomiting and fever. Most people recover in a few days, but they must replace lost water and salts. Infants, older people and people with weakened immune systems can become seriously ill if the bacteria enter the blood.Prevention. Cooking food thoroughly kills the bacteria. Other measures include keeping food in a fridge below 5 °C, keeping raw and cooked food apart, washing hands after handling raw meat, and vaccinating hens against Salmonella, as is done in the UK.