Scientists from EMBL’s Bork group, in collaboration with the Zeller team and the Luxembourg Centre for Systems Biomedicine, have identified many shared microbial strains in saliva and stool samples from several hundred people across three continents. Their research, published in eLife, shows that the barrier between oral and gut microbiomes is weaker than expected and highlights evidence of oral-gut transmission of several microbes thought to play direct roles in the progression of colorectal cancer.
The mouth and the gut are abundantly colonised by microbes and linked by a constant flow of food and saliva. Despite this, they host distinctly different microbiomes. The acidic stomach and antimicrobial small intestine form an oral-gut barrier which was thought to kill off the vast majority of oral microbes before they reached the gut.
Oral-gut transmission occurs when enough cells of an oral species survive the population bottleneck of the oral-gut barrier to establish a new colony inside the gut. This barrier failure has previously been considered rare and – when it does happen – associated with various diseases.
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