GI Microbiome Dysbiosis and Enterococcal Overgrowth During GVHD. Stool samples were collected serially from patients after allogeneic HCT, and the 16s bacterial RNA was analyzed by pyrosequencing. Samples from patients without GVHD (n=65) showed four phyla (firmicutes, bacteroidetes, actinobacteri, and proteobacteria) representing almost 75 percent, with enterococci accounting for about 25 percent. Samples from patients with GVHD (n=6) showed marked dysbiosis and dramatic overgrowth of enterococci, now representing 75 percent, with all other phyla accounting for only 25 percent (p < 0.002).