Mutagen formation by intestinal bacteria

Abstract

In the past several years much attention has been given to the correlation between intestinal microflora and the formation of colonic cancer. One area of specific interest has been the correlation of microflora to cocarcinogens produced from dietary components through interference with intestinal bacteria (Drasar and Hill, 1974). However, no clear evidence for this correlation has yet been obtained. This communication reports on the isolation and chemical characterization of indole derivatives from several intestinal bacteria and their DNA-damaging activity. Suzuki and Mitsuoka (1978) reported that high mutagenic activities exist in the cell-free homogenates prepared from the intestinal bacteria belonging especially to Streptococcus faecium, Veillonella parvula, Peptostreptococcus parvulus, Veilloneila alaclescena, Bacterioides multiacidus and Eubacterium limosum. Cultures of each of these six strains were made by using a modified liquid EG medium under anaerobic conditions (Suzuki and Mitsuoka, 1978; Parker, 1955) and incubated at 37°C for 3 days. After incubation, the cultures were extracted with ethyl acetate. DNA-damaging activity and mutagenicity were assayed by the rec assay with Bacillus subtilis strains HI7 rec ÷ and M45 rec(Kada et al., 1972), as well as by bacterial reversion assays with Salmonella typhimurium strains TAI00, TA98 and TA1535 (Ames et al., 1975). Preliminary experiments showed that most of the active products were extracted with ethyl acetate. As shown in Table 1, high DNA-damaging activities were found in the ethyl-acetate extracts obtained from Streptococcusfaecium IB 37, Veillonella parvula ATCC 10790 and Eubacterium limosum ATCC 8486 as shown by the differential growth inhibition between the Rec ÷ and Recstrains. However, none of the ethyl-acetate extracts showed mutagenic activity in the Ames assay with strains of TAI00, TA98 and TA1535 in the wide dose range of 20-2000 #g/plate. However, Suzuki and Mitsuoka (1978) had observed marked mutagenic activities with strain TA1535, in the cell-free homogenates prepared from S. faecium IB 37, V. parvula ATCC 10790 and B. multiacidus ATCC 27723. One possibility for this difference