As part of the multicentre, prospective observational study TIARA (The impact of colonisation with MDRO in complex surgical patients), a cohort of 1,200 patients undergoing open or laparoscopic procedures for partial or complete removal of the pancreas/duodenum (pancreaticoduodenectomies), colon (colon resections) or rectum (rectal resections) will be included at eight German university hospitals over a period of five years. During the observation period of these patients, a comprehensive collection of clinical data and biomaterial samples (e.g. by means of wound and nasal swabs) takes place before, during and after the operation at specified times.