Study Finds the Mouth’s Mix of Microbes Differs Based on Ancestry

Nov. 26, 2019

Hundreds of microbial taxa colonize the teeth, tongue, cheeks, palates, tonsils and other hideaways of the human mouth. Oral-dwelling bacteria have been tied to problems like cavities and periodontal disease, and they may encode clues about other disease risks as well. They also play integral roles in regulating the immune system and absorbing nutrients. 

mSystems: Racial Differences in the Oral Microbiome: Data from Low-Income Populations of African Ancestry and European Ancestry.

But not every mouth hosts the same microbial mix. An analysis of mouth rinse samples collected from more than 1,600 low-income people in the southeastern United States, published this week in mSystems, found significant differences in oral microbiome composition between African-Americans and European-Americans. Notably, African-American participants hosted more diverse populations.

“These findings call for research to understand how the racial difference in oral microbiome influences the health disparity,” the authors noted in the study.

The researchers identified 32 individual taxa—including some pathogens tied to periodontal disease—that differed significantly in abundance between the 2 races. For example, African American participants hosted a higher abundance of Bacteroidetes, species of which are common in the gut, and lower abundances of Actinobacteria and Firmicutes bacteria. Four rare pathogens associated with periodontal disease were more prevalent in African-Americans than in European-Americans. 

Such differences could help elucidate connections between the microbiome and disease risk, as well. In previous work by the same group, for example, using data from the same cohort, the researchers found that people with higher levels of Actinobacteria in their oral microbiome had a lower risk of type II diabetes. 

Other studies have reported finding differences in the microbiomes of the gastrointestinal tract, skin and vagina based on ancestry; a few have also reported finding differences in oral microbiomes. In one, published in 2013 in PLOS One, researchers analyzed saliva samples from 192 people representing 4 ethnicities: non-Hispanic blacks, non-Hispanic whites, Chinese, and Latinos. Another study, published in 2014 in BMC Microbiology, involved 152 samples collected from people in Alaska, Germany, and Africa. 

Those studies found that the African-Americans had less, not more, diverse oral microbiomes, which is contrary to the new study. The mSystems authors hypothesize that because those earlier investigations involved small study populations, or used lower resolution gene sequencing tools, they may not have detected less prevalent microbes in the samples. 

The new study is the largest, to date, to investigate ethnic differences in the oral microbiome, the researchers noted. It included 1,058 African-Americans and 558 European-Americans, all adults who had enrolled in the Southern Community Cohort Study, a long-running prospective study funded by the National Cancer Institute. Jirong Long, Ph.D., an epidemiologist at Vanderbilt University in Nashville, Tennessee, worked on the new study and has previously used data from the same cohort to probe the link between the oral microbiome and risk of colorectal cancer.

Long and her colleagues cautioned that while the new analysis suggests promising new avenues of investigation, further studies are needed—using shotgun metagenomic sequencing, for example—to better understand racial differences at the species level.

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Author: Stephen Ornes

Stephen Ornes
Stephen Ornes is a science and medical writer who lives in Nashville, Tennessee. He's also the creator and host of "Calculated," a podcast collection of stories about people at the intersection of math, art and culture. Visit him online at