Hi, Stefan, > Also I read in the newspaper, that beneficial bacteria of the species > E-Coli are normally harmless and needed in the intestines, but can > become dangerous for people with weakened immune system, especially > AIDS patients. The problem with the species E. coli is that there are "beneficial" strains which are part of the normal intestinal flora and others which have aquired a whole lot of virulence factors. The latter ones can cause severe intestinal and/or extraintestinal diseases. Perhaps you have heard or read somewhere of ETEC = enterotoxigenic E. coli EPEC = enteropathogenic E. coli EIEC = enteroinvasive E. coli STEC = Shiga Toxin-producing E. coli EHEC = enterohemorrhagic E. coli These are NOT benevolent strains and you don't necessarily need to have a weakened immune system to get infected with them. Best regards, Sylvia Franke