Dietary ginseng alters the composition of the bacterial flora while intraperitoneal compound K inhibits colon cancer xenograft growth. A. Compound K inhibits colon cancer growth in tumor xenograft. HCT116 cells (5*10^6 cells) were implanted into flanks of nu/nu mice and allowed to grow for 5 days. Mice were then treated with compound K (30 mg/kg-body wt or DMSO (compound K vehicle). At indicated times tumor size was estimated by linear dimensions [volume = 1/2 × length × (width)2] and expressed in mg (*p < 0.05 compared to control, n = 5 mice in each group). B. Rb1 absorption. Mice were un-treated or treated with metronidazole in the drinking water. After 5 days animals were gavaged with 500 mg ginseng extract/kg body wt. At indicated times after ginseng gavage, plasma levels of ginsenoside Rb1 were measured by UPLC-mass-spectrometry/TOF. C. Compound K absorption. Mice were treated as described in 4B and Compound K (C-K) measured by UPLC-mass-spectrometry/TOF. Data were expressed as means ± SEM depicted by vertical bars (p < 0.05 compared to mice not receiving antibiotics). Note that metronidazole suppressed serum compound K but not Rb1 levels. D. Effects of ginseng on bacterial phyla. Mice were fed Western diet or Western diet containing 250-ppm ginseng. After 2 wks feces were collected and bacterial DNA extracted. Using 16S rRNA gene libraries, bacteria were classified by phyla as described in "Materials and Methods". E. Principal coordinate analysis (PCA) of bacterial distributions. Note that ginseng decreased the abundance of Tenericutes phylum and appeared to widely separate species as assessed by PCA.