Feb 27, 2009 - News

The Mix of DNA in a Saliva Sample

Each of us is made up of about 50 trillion cells, which is pretty mind-blowing until you consider the number of microbial cells living on or in each of us.   It’s estimated that a healthy adult is lugging around 10 times more bugs. Most of them are bacteria rather than human cells.

Just as the tiny differences we each harbor in our DNA can reveal information about our health and our ancestry. It might also reveal the subtle differences in the types of bacteria we all carry.

Human Microbiome

The NIH has initiated a large project to explore the so-called “human microbiome” and its implications for our health.   Other projects are using bacteria to trace ancient migrations and human interactions.

Today scientists published the first in-depth study of global diversity in a specific human microbiome — the mouth. There is wide variety around the world in dietary and other cultural factors that could influence the types of bacteria found in a person’s mouth. However, the researchers discovered that the an individual’s “salivary microbiome” is likely to be just as different from a neighbor’s as it is from someone on the other side of the world.

“[T]here is significantly more diversity in bacterial genera [types of bacteria] compared from different individuals than from the same individual,” the authors write. “[But] the diversity among individuals from the same location is nearly the same as the diversity among individuals from different locations.”

Their results appear online in Genome Research.

Oral Bacteria

The researchers studied the oral bacteria of 120 people — 10 individuals from each of 12 worldwide locations: Oakland, CA; Baton Rouge, LA; La Paz, Bolivia; Buenos Aires, Argentina; Pointe Noire, Congo; Johannesburg, Sought Africa; Surigao, Philippines; Shanghai, China; Batumi, Georgia; Ankara, Turkey; Warsaw, Poland; and Dessau/Leipzig, Germany.

Overall, DNA analysis identified a total of 101 known types of bacteria. Thirty-nine of those had not previously been found in the human mouth.   The scientists also found evidence for another 64 unknown bacterial types lurking in people’s mouths.

Their results lay the groundwork for future studies that will explore the influence of environmental, dietary and genetic factors on the types of bacteria found in a person’s saliva.   This may lead to a better understanding of the role of saliva bacteria in mouth diseases. It can also shed light on the interaction of the salivary microbiome with other microbial environments in the body, such as the intestines.

Their work could also help expand the use of bacteria in the study of human history. The stomach bacteria H. pylori has already been used in several studies to investigate human history. Just last month a study using this bacteria revealed new information about how Polynesia was colonized.   But while these H. pylori studies have been impressive, they do have a downside: a stomach biopsy is needed to get the samples.

“There would be obvious advantages if similarly-informative bacterial species could be identified in saliva,” the authors write, suggesting that their work might help identify just such a species.

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