Effect of intestinal bacteria on incidence of liver tumors in gnotobiotic C3H/He male mice.

The effect of intestinal microflora on liver tumorigenesis was studied in gnotobiotic C3H/He male mice monoassociated, diassociated, or polyassociated with the following strains of intestinal bacteria: Escherichia coli, Streptococcus faecalis, Bifidobacterium adolescentis, Bifidobacterium infantis, Clostridium indolis, C. paraputrificum, C. perfringens, C. innocuum, C. nexile, C. ramosum, C. clostridiiforme, Bacteroides multiacidus, Bacteroides fragilis, Veillonella alcalescens, V. parvula, and Lactobacillus acidophilus. The incidence of liver tumors was higher in most of the gnotobiotes (67--100%) and conventionalized mice (82%) derived from the germfree mice than in the germfree mice (39%). The average incidence of tumor nodules in gnotobiotes associated with E. coli, S. faecalis, and C. paraputrificum was 2.9, which was significantly higher than that in the conventionalized animals (1.6). In contrast, the average incidence of tumor nodules in gnotobiotes associated with E. coli, S. faecalis, L. acidophilus, C. perfringens, and Bacteroides fragilis (0.9) was not significantly different from that in germfree animals (0.5). The present study demonstrated that the presence of certain intestinal bacteria is related to liver tumorigenesis in gnotobiotic C3H/He male mice.