Clostridium difficile bacteria. Coloured scanning electron micrograph (SEM) of dividing C. difficile bacterial cells (yellow). Old dead bacterial cells are pink. These rod-shaped bacteria cause pseudomembranous colitis, one of the most common hospital-acquired infections, and antibiotic-associated diarrhoea. Infection can be fatal. Treatment is with antibiotic drugs, although this bacterium has become increasingly resistant to the use of antibiotics.