The present invention relates to a new isolated polypeptide nominated microcin S, isolated nucleic acid molecules encoding the microcin S polypeptide and primers and probes hybridizing to the nucleic acid molecules. The invention also relates to plasmids and cells comprising the nucleic acid molecules, an antibody binding to the polypeptide, compositions as well as methods for producing and using the polypeptides. The present invention further relates to medical uses for treating or preventing microbial infections, functional gastrointestinal disorders or treating a tumor. The invention further relates to a method for preserving food and a method for coating dressing material.