Studies on the colonic bacterial flora during experimental carcinogenesis induced with N-methyl-N'nitro-N-nitrosoguanidine.

The study was carried out on 72 rats receiving during 7 weeks rectal infusions of N-methyl-N'nitro-N-nitrosoguanidine (MNNG), a carcinogenic agent. During the follow-up of 52 weeks the changes were investigated in the quantitative composition of the aerobic and anaerobic bacterial flora of the large intestine, and the basic composition of the aerobic flora was established. It was found that MNNG modified the quantity and composition of the bacterial flora of the colon not only with a reduction in the number of bacteria in the faeces but also with a transient change in the composition and proportions of various bacterial species. Attention is called to the observation that the appearance and development of malignant tumours in the large intestine was connected with a rise in the number of micro-organisms correlated with the histological transformation of the colonic mucosa and the number of tumours in it.