Clostridium difficile bacteria growing on agar. Infection by this bacteria can cause diarrhoea and inflammation that could lead be fatal. Antibiootic treatment is complicated by the development of antibiotic resistant strains. In such cases, faecal microbiota transplantation (FMT) is considered as a last resort, but one with a high rate of success. Photographed at Guy's and St Thomas' hospital, London, UK.