Faecal bacterial flora in cancer of the colon.

Selective aerobic and anaerobic plate media were employed to isolate the predominant faecal flora of patients with cancer of the colon (CC), cancer with non-gastrointestinal involvement (NGI), and with non-malignant diseases (N). The CC and N groups did not differ significantly in either total aerobic or anaerobic counts. The CC group did have a significantly lower anaerobic/aerobic ratio compared with the N group (2.42 vs. 2.96, P less than 0.05). This was the result of a greater predominance of aerobic bacteria and a decrease in anaerobic cocci, Eubacterium and Fusobacterium in the CC group. Previous studies report that aerobic organisms have a greater ability to produce amines than non-spore forming anaerobes. If the intestinal flora can produce carcinogenic nitrosamines in vivo from amines and nitrites, the aerobic bacterium in the faeces may be of importance in supplying the amine substrate for nitrosation. The comparison of the NGI group with the N group showed a significant variation in the total anaerobic count (11.02 vs. 11.41, P less than 0.05) and in the composition of the faecal flora. This indicates that discretion must be used in analysing the data obtained from cancer patients, as the presence of a carcinoma may be responsible for changes in bacterial flora.