Clostridium difficile bacteria, coloured scanning electron micrograph (SEM). These rod-shaped bacteria cause pseudomembranous colitis, one of the most common hospital-acquired infections, and antibiotic-associated diarrhoea. The infection is often caught from bacterial spores, which it forms in unfavourable conditions. When a patient takes a course of antibiotics the normal flora in their gut is killed off, allowing C. difficle to colonise it. It produces 2 toxins, which cause inflammation of the intestinal wall (colitis) with diarrhoea, abdominal pain and fever. Infection can be fatal. Treatment is with antibiotics, although it is becoming increasingly resistant to them. Magnification: x3000 at 10 centimetres wide.