Effect of a biological response modifier, PSK, on intestinal flora of tumor-bearing mice.

PSK, a protein-bound polysaccharide derived from basidiomycetes, is a biological response modifier that exhibits a variety of activities following oral administration, including prevention of infection. In this study, the effects of oral administration of this drug on microbial flora of tumor-bearing mice were examined. Numbers of Staphylococcus, Streptococcus and Pseudomonas were increased, and those of Bifidobacterium and Lactobacillus were reduced in fresh feces of mice from later than 9 weeks after inoculation of sarcoma 180. However, these changes were prevented by oral administration of PSK. In mice bearing sarcoma 180, the increases in numbers of Staphylococcus and Pseudomonas and the decrease in those of Bifidobacterium were further enhanced by intraperitoneal administration of anticancer agent mitomycin C, but such changes were suppressed by oral administration of PSK. These results suggest that PSK has a preventive effect against abnormal conditions of the intestinal flora induced by tumor inoculation or the administration of anticancer agents.