The bacteria in the human mouth – particularly those nestled under the gums – are as powerful as a fingerprint at identifying a person's ethnicity, new research shows

Scientists identified a total of almost 400 different species of microbes in the mouths of 100 study participants belonging to four ethnic affiliations: non-Hispanic blacks, whites, Chinese and Latinos. Only 2% of bacterial species were present in all individuals – but in different concentrations according to ethnicity – and 8% were detected in 90% of the participants. Beyond that, researchers found that each ethnic group in the study was represented by a "signature" of shared microbial communities. "This is the first time it has been shown that ethnicity is a huge component in determining what you carry in your mouth. We know that our food and oral hygiene habits determine what bacteria can survive and thrive in our mouths, which is why your dentist stresses brushing and flossing. Can your genetic makeup play a similar role? The answer seems to be yes, it can," said Purnima Kumar, associate professor of periodontology at The Ohio State University and senior author of the study. "No two people were exactly alike. That's truly a fingerprint." Kumar used a DNA deep sequencing methodology to obtain an unprecedented in-depth view of these microbial communities in their natural setting. When the scientists trained a machine to classify each assortment of microbes from under the gums according to ethnicity, a given bacterial community predicted an individual's ethnicity with 62% accuracy. The classifier identified African Americans according to their microbial signature correctly 100% of the time. The findings could help explain why people in some ethnic groups, especially African Americans and Latinos, are more susceptible than others to develop gum disease. The research also confirms that one type of dental treatment is not appropriate for all, and could contribute to a more personalized approach to care of the mouth. "The most important point of this paper is discovering that ethnicity-specific oral microbial communities may predispose individuals to future disease," Kumar said. Though it's too soon to change dental practice based on this work, she said the findings show that "there is huge potential to develop chair-side tools to determine a patient's susceptibility to disease." Using only the bacteria found under the gums – which are called subgingival microbes – the classifying machine performed best at positively identifying African Americans according to their microbial communities, followed by positive identifications of Latinos at 67% and whites at 50% – but with 91% specificity, meaning the classifier determined how often a sample did not come from a white person 91% of the time. Kumar and colleagues then expanded the selection of total microbes in all areas of the mouth, and identified surrogate communities of bacteria that were present in at least 80% of participants of each ethnic group. These communities showed a prediction likelihood of 65% for African Americans, 45% for whites, 33% for Chinese and 47% for Latinos. "Nature appears to win over nurture in shaping these communities," Kumar noted, because African Americans and whites had distinct microbial signatures despite sharing environmental exposures to nutrition and lifestyle over several generations.