AsianScientist (Nov. 21, 2017) – A team of researchers at Waseda University in Japan have demonstrated that bacteria in saliva can cause inflammation in the intestine. They reported their findings in Science.
On average, humans ingest 1.5 liters of saliva containing bacteria every day. Although the effects of oral bacteria in the mouth have been relatively well studied, the impact of oral bacteria on gut health remains unknown.
In this study, a team of scientists led by Professor Masahira Hattori of Waseda University found that oral microbes are responsible for activating immune cells in the gut, resulting in inflammation that potentially leads to inflammatory bowel disease (IBD).
The scientists first administered salivary samples of healthy and IBD-afflicted individuals to germ-free mice which do not harbor bacteria in their intestines. After six to eight weeks, they analyzed the microbial content of the mice’s feces with 16S ribosomal RNA gene sequencing and found approximately 20 kinds of oral bacteria in the feces.
Immunological analysis revealed that the level of TH1 cells, characteristically expressing interferon-gamma protein, was elevated in mice receiving saliva from IBD-afflicted individuals. The TH1 cells activated macrophages, and prolonged macrophage activation resulted in gut inflammation.
To survey exactly which bacteria induced TH1 cells in the gut, researchers isolated and cultured the microbes from the feces, then separately inoculated each microbe in germ-free mice. They found that Klebsiella pneumoniae, which is usually a harmless resident in the mouth of healthy individuals, was a strong inducer of TH1 cells when they colonized the gut. Further experiments demonstrated that a molecule called interleukin-10 could suppress inflammation caused by em>K. pneumoniae colonization of the gut.
These findings suggest a profound association between oral microbes and the microbial ecosystem of the gut, paving the way for novel types of therapeutics in the treatment of chronic inflammatory diseases.
“Although more research needs to be done, our results will help the development of very narrow spectrum antibiotics, such as lytic bacteriophages, that specifically target K. pneumoniae,” said Hattori.
The article can be found at: Atarashi et al. (2017) Ectopic Colonization of Oral Bacteria in the Intestine Drives TH1 Cell Induction and Inflammation.
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Source: Waseda University; Photo: Shutterstock.
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