Studies indicate creatinine can be effective at killing bacteria of many species in both the Gram positive and Gram negative as well as diverse antibiotic resistant bacterial strains. Creatinine appears not to affect growth of fungi and yeast; this can be used to isolate slower growing fungi free from the normal bacterial populations found in most environmental samples.  The mechanism by which creatinine kills bacteria is not presently known.  A recent report also suggests that creatinine may have immunosuppressive properties.