Abstract: It has been known that there is a close correlation between the genotoxic effect of chemicals on the bacteria and their mutagenesis or carcinogenesis on mammals. In order to investigate the mechanisms of the anticarcinogenicity effect of Bifidobacteria , the inhibitor effect of Bifidobacterium bifidum(Bif1101) and it s surface molecules - Lipoteichoic acid (L TA) , whole cell peptidoglycan (WPG) and Spent Culture (SC) on the SOS reaction of E. coli PQ37 induced by N-methyl2N′2nit ro2N2nit rosoguanidine (MNN G) was studied. The result s indicate that all of the tested Bifi1101 related materials appeared significant inhibition on the SOS response induced by MNN G, but the most effective component s was L TA , the following WPG, Bif1101 , SC. The uninoculated BL medium had not appeared effect of antimutagenicity. This kind of in vit ro antimutagenicity of Bifidobacteria and it s surface is probably occured by binding or cleaving the active center of mutagens.

Key words: Bifidobacterium bifidum, lipoteichoic acid, Whole Cell peptidoglycan, Antimutagenicity, MNNG