Salmonella bacterium. Coloured transmission electron micrograph (TEM) of the bacterium Salmonella typhimurium, a flagellate, rod-shaped, Gram-negative bacterium. The flagellae (thread- like structures) are used for movement. S. typhimurium is a major cause of food poisoning (salmonellosis) in humans. Salmonella bacteria are transmitted in food. Infections are common in poultry and eggs. Inadequately cooked pork and beef are also potential sources. Rats and mice are also common carriers. Clinical symptoms are headache, fever, abdominal pain and diarrhoea. Magnification: x23,500 when printed 10cm wide.