Table 3.

Specific microorganism or dysbiosis of microbiome in colorectal cancer

Specific microorganism or dysbiosis of the microbiome	Findings (References)
Colorectal cancer
Oral microbes	Members of oral microbes, including Gemella, Peptostreptococcus, Parvimonas, and Leptotrichia, were enriched in colorectal adenocarcinoma tissue (Nakatsu et al. 2015). Members of oral microbes, including Parvimonas micra, Peptostreptococcus stomatis, and Peptostreptococcus anaerobius, were enriched in fecal specimens from patients with metastatic colorectal adenocarcinoma (Thomas et al. 2019; Wirbel et al. 2019; Yachida et al. 2019). Peptostreptococcus anaerobius can activate the NFKB signaling pathway in colorectal cancer cell lines and inhibit T-cell-mediated immune responses against colorectal tumors through the recruitment of myeloid-derived suppressor cells and tumor-associated macrophages into the tumor microenvironment in the ApcMin/+ mouse model (Long et al. 2019).
Viral microbiome	Some specific viral taxa, such as Orthobunyavirus, Inovirus, or Tunalikevirus, were enriched in fecal specimens from patients with colorectal cancer, and dysbiosis of intestinal viral microbiome was associated with worse clinical outcomes in colorectal cancer (Nakatsu et al. 2018).
Fungal microbiome	The amount of Malasseziomycetes was increased, while the amounts of Saccharomycetes and Pneumocystidomycetes were decreased in fecal specimens from patients with colorectal cancer compared to cancer-free individuals (Coker et al. 2019).
Fusobacterium nucleatum	The amount of Fusobacterium nucleatum was increased in tumor tissue and fecal specimens from patients with colorectal cancer (Mima et al. 2017). Fusobacterium nucleatum was detected not only in primary colorectal tumors, but also in metastatic lymph nodes and liver metastases (Bullman et al. 2017; Yu et al. 2016). Fusobacterium nucleatum can inhibit T-cell-mediated immune responses against colorectal tumors through the recruitment of myeloid-derived suppressor cells into the tumor microenvironment in the ApcMin/+ mouse model (Kostic et al. 2013). The Fap2 protein of Fusobacterium nucleatum has been shown to interact with T cell immunoglobulin and ITIM domain receptor and inhibit activities of NK cells and T cells (Gur et al. 2015).
Campylobacter species	The amount of Campylobacter species was enriched in colorectal cancer tissue and fecal specimens from patients with colorectal cancer (Warren et al. 2013; Wu et al. 2013).
Escherichia coli	Escherichia coli was enriched in colorectal cancer tissue (Bonnet et al. 2014; Kohoutova et al. 2014).
Bacteroides fragilis	Bacteroides fragilis was enriched in colorectal cancer tissue (Boleij et al. 2015; Toprak et al. 2006; Wei et al. 2016). Enterotoxigenic Bacteroides fragilis induces T helper 17 cells, which activate the STAT3 signaling pathway in tumor cells in the ApcMin/+ mouse model (Wang et al. 2009; Wu et al. 2009).
Enterococcus faecalis	Enterococcus faecalis was detected significantly more often in fecal specimens from colorectal cancer cases than controls (Balamurugan et al. 2008).
Streptococcus gallolyticcus	The amount of Streptococcus gallolyticcus in human colorectal carcinomas was higher than in control tissue (Abdulamir et al. 2010; Boleij and Tjalsma 2013; Gupta et al. 2010).