Coloured scanning electron micrograph (SEM) of Salmonella infantis bacteria. These rod-shaped, motile, Gram-negative bacteria cause the foodborne disease salmonellosis. Infection causes fever, abdominal cramps, and diarrhoea, which is sometimes bloody. Occasionally these bacteria establish a localised infection such as reactive arthritis, which causes inflamed joints. Systemic spread of the bacteria can lead to sepsis, which can be life threatening. Treatment is with antibiotics, although resistant strains are becoming more common. Magnification: x1,900 when printed at 10 centimetres wide.