Stool sample for faecal transplantation. Faecal microbiota transplantation (FMT) is offered as a last resort when other treatments have failed to treat Clostridium difficile infection. Donors are screened and tested before samples are accepted. Stool samples are diluted in saline, filtered and the bacteria preserved with the addition of glycerol before storage at minus 80 degrees Celsius. FMT restores the healthy balance of bacteria in the colon. Photographed at Guy's and St Thomas' hospital, London, UK.