Akkermansia muciniphila in the Human Gastrointestinal Tract: When, Where, and How?

Akkermansia muciniphila is a mucin-degrading bacterium of the phylum Verrucomicrobia. Its abundance in the human intestinal tract is inversely correlated to several disease states. A. muciniphila resides in the mucus layer of the large intestine, where it is involved in maintaining intestinal integrity. We explore the presence of Akkermansia-like spp. based on its 16S rRNA sequence and metagenomic signatures in the human body so as to understand its colonization pattern in time and space. A. muciniphila signatures were detected in colonic samples as early as a few weeks after birth and likely could be maintained throughout life. The sites where Akkermansia-like sequences (including Verrucomicrobia phylum and/or Akkermansia spp. sequences found in the literature) were detected apart from the colon included human milk, the oral cavity, the pancreas, the biliary system, the small intestine, and the appendix. The function of Akkermansia-like spp. in these sites may differ from that in the mucosal layer of the colon. A. muciniphila present in the appendix or in human milk could play a role in the re-colonization of the colon or breast-fed infants, respectively. In conclusion, even though A. muciniphila is most abundantly present in the colon, the presence of Akkermansia-like spp. along the digestive tract indicates that this bacterium might have more functions than those currently known.