Several projects of this collaborative research centre (SFB) study the influence of the bacterial flora on the gut mucosa, respectively analyse whether certain probiotics do exert a protective effect against pathogens. Along with genetic factors the individual resident luminal gut flora to a considerable degree is influencing the reaction pattern of the intestinal mucosa. For several projects the availability of hygienically defined, i.e. gnotobiotic laboratory animals are indispensable. The Z1 project therefore will rederive genetically modified mouse strains developed by these groups and if necessary maintain these amongst others (e.g. BALB/c; C57BL/6J; B6.129P2- Il10tm1Cgn; C3H/H3BirJ; C3Bir.129P2(B6)-Il10tm1Cgn) as axenic nuclei in isolators. Moreover, these strains will be associated with pathogenic and probiotic germs under controlled conditions. The Z1 project thus functions as a central gnotobiotic animal facility for the SFB.