Antitumor effect of normal intestinal microflora on Ehrlich ascites tumor

In order to investigate the antitumor activity of intestinal microflora, the constitution of normal flora was examined in humans, guinea pigs and mice. It was clarified that Eubacterium, Bifidobacterium and Bacteroides were the predominant bacterial genera in humans. In addition, neither Clostridium nor Enterobacteriaceae was detected in guinea pigs and neither Clostridium nor Bifidobacterium was present in mice. Total bacterial counts in tumor-bearing mice were reduced in comparison with those in normal mice. Especially, in the ileum of tumor-bearing mice, the incidence of anaerobic bacterial genera was strikingly decreased. From the bacteria found, 59 living and killed strains isolated from intestinal microflora were examined for antitumor activity against Ehrlich ascites tumor. It was observed that 11 of the tested strains had antitumor activity. Four of these were toxic to the host, and in particular, all mice injected with Pseudomonas aeruginosa (TYM-8) died within several days. Eubacterium lentum (TYH-11), Propionibacterium acnes (TYM-28), Proteus mirabilis (TYM-7) and Serratia marcescens (TY-142), in which antitumor activity was recognized with living and formalin-killed bacteria, cured the tumor-bearing mice, and the culture supernatant of S. marcescens contained apparent antitumor activity.