Gross! Scientists Find More Than 10,000 Species Of Germs On The Human Body
June 14, 2012

Gross! Scientists Find More Than 10,000 Species Of Germs On The Human Body

Lawrence LeBlond for

Take a much closer look at the human body and you might see something you perhaps didn´t expect to find: a community of more than 10,000 different species of germs and bacteria, making their home on our skin, in our mouths, up our noses, and in our gut.

While you may squirm at the thought of having so many germs crawling in, on, over and around your body, scientists are quick to point out that not all these germs are bad. In fact, researchers have looked into more than 100 trillion germs that make their home on the human body that are actually beneficial to our existence.

Until now, nobody really knew that much about these germs. But, according to scientists working for the Human Microbiome Project, they are essential for human life; they are needed to digest food, to synthesize vitamins, and form barriers against harmful bacteria, among other things.

Working to find out just what role these germs play in our existence, and to what variation they occur from individual to individual, scientists from more than 80 different institutions have mapped all the creatures that are normally found living on or in us.

The five-year federal effort was funded by the National Institutes of Health and consisted of more than 200 scientists sequencing the genetic material of bacteria found on nearly 250 healthy people. What they found was more strains than they had ever imagined -- as many as a thousand bacterial strains on each person, with each person having a different mix of microbes than the next.

Surprisingly, they also found that nearly everyone harbors low levels of harmful bacteria known to cause specific infections. However, in healthy people, like the ones tested, these bugs simply coexisted in a peaceful manner with their benign counterparts.

The project, published in the journal Nature, as well as three separate PLoS journals, adds a significant piece to the human health puzzle. Just as the Human Genome Project worked to map thousands of human genes, the Human Microbiome Project sought to map the number of microbes on our bodies. Understanding how these microbes work, and what role they play could lead to new strategies in fighting diseases such as chicken pox, the common cold, and even athlete´s foot.

This project is a “revelation,” said John Baker, a professor of surgery at the Medical College of Wisconsin. “I think until five years ago we really were not thinking about the microbiome in terms of health and disease“¦ As this project evolves, it´s going to give us so much more information about what it means to be human.”

This work is “giving us for the first time this map in terms of microbes, who´s there, who´s living on our skin, who´s living in our intestines. Then, when we know who´s there, we can start to ask what they´re doing,” said Baker.

Scientists say the next step will be to explore why the bad microbes harm some people but not others. What changes a person´s chemistry that puts them at risk for certain diseases? The findings are already giving scientists a clearer picture.

“This is a whole new way of looking at human biology and human disease, and it´s awe-inspiring,” lead researcher Dr. Philip Tarr of Washington University at St. Louis told the Associated Press (AP). “These bacteria are not passengers. They are metabolically active. As a community, we now have to reckon with them like we have to reckon with the ecosystem in a forest or a body of water.”

And like an environmental ecosystem, each persons´ microbial makeup varies greatly by body part. The skin could be a rainforest, filled with numerous species, while your gut teems with distinctly different species, much like an ocean, Tarr explained.

Scientists have long known that our bodies coexist with literally trillions of germs, but have never studied them on this level before. Most researchers have only studied germs that cause disease, such as Staphylococcus aureus, which lives harmlessly in one person´s nose or on skin, but can be deadly if it infects another individual.

Now, scientists have taken the step to map out the entire human microbiome in a big way.

The scientists first collected tissue samples from more than a dozen sites on the human body of each individual -- the mouth, nose, different areas of skin, privates, and from feces. Secondly, the teams teased apart the bacterial DNA from the human DNA, and then analyzed the organisms they collected.

Dr. Eric Green, director of NIH´s National Human Genome Research Institute, said that our bodies are home to about 10 bacterial cells for every human cell, but because they are so small, they only make up about 1 to 3 percent of our body mass. This means that a 200-pound person has about 6 pounds of bacteria on their body.

The project estimated that there are about 8 million microbial genes in our body, exponentially more than the 22,000 human genes. Those bacterial genes produce substances that perform very specific jobs in our system, some of which play a crucial role in our well-being, Dr. Bruce Birren, of the Broad Institute of MIT and Harvard, who was part of the mapping project, told AP's Lauran Neergaard.

While these germs play a critical role in our health, they can vary dramatically depending on where we live, what we eat, and many other factors. Your microbial zoo can change, for example, when you take antibiotics to kill infection-causing germs as well as good intestinal bacteria that may be replaced with different but equally effective bacteria.

“We don´t all have the same bacteria although they all seem to have been organized to do the same things,” Birren said, adding that it may be that our lifestyle and environment “induces each of us to have arrived at a solution that works for us.”

“Now we have to say, ℠OK pathogens happen, but (disease) may happen because germs are not in a healthy ecosystem,´” said Tarr. Until now, learning about microbes has proved to be a challenge.

“Even today, we are unable to grow the vast majority of microbes that live in and on us in the laboratory," said Green.

The microbiome project, however, now leaves scientists with a very different challenge.

“The information,” said Baker, “is overwhelming.”

All this new information shows just how much work is needed to understand this strange world living within us, noted infectious disease specialist Dr. David Relman of Stanford University, who wrote a review of the project´s findings for the journal Nature.

There exists many remaining questions about how these microbes interact with human genetics, he wrote. “We are essentially blind to many of the services that our microbial ecosystems provide – and on which our health depends.”