<p>Prion diseases are fatal and contagious brain disorders caused by a pathogenic prion protein (PrP^Sc) derived from the benign prion protein (PrP^C). To date, there are no therapeutic substances to completely block prion diseases. Thus, the development of a therapeutic substance is necessary, and the identification of a novel biomarker of prion disease is the first essential step to develop new drugs. In the present study, we carried out a metagenomic analysis to identify microbiome biomarkers for prion disease using next-generation sequencing and bioinformatics tools in intraperitoneally prion-infected mice. In addition, we evaluated the protective effects of epigallocatechin-3-gallate (EGCG), a potent microbiome changer, in prion-infected mice by western blotting and survival analysis. We found a total of 14 differentially abundant taxa between prion-infected and control mice. In addition, we found that prion diseases caused altered microbiome networks and upregulation of DNA repair-related pathways. Furthermore, we observed the protective effect of the microbiome changer EGCG against prion disease in prion-infected mice. Given previous reports of microbiome alterations in prion diseases, we further validated these associations and demonstrated the protective effects of a microbiome-modulating compound.</p>