Surprising Benefits of Bacteria: The Human Microbiome

The Benefits of Bacteria

These days you can hardly find a hand soap that doesn't tout its antibacterial properties, and Purell has taken up permanent residence in many of our purses. So it's understandable if learning that you have three to five pounds of microbes in and on your body makes you feel a bit green. "In the past we tended to think that the absence of microbes made people healthy," says microbial ecologist Lita Proctor, PhD. "But as we're learning, bacteria are not just a source of disease—they're a source of health."

Proctor directs the NIH-funded Human Microbiome Project (HMP), which last summer released the results of a five-year endeavor to identify and sequence the genetic material of all the microbes living in 242 healthy people. So far, HMP's data show that the average person plays host to more than 10,000 species of organisms, including bacteria, viruses, and fungi. All together, these make up what scientists refer to as your microbiome.

Every person's microbiome is unique—the product of their genes, the foods they eat, and the environment they're exposed to. But people who share certain physical and neurological traits also have similar microbiomes. Obese people's microbiomes look different from lean people's; kids with autism have a different type of bacteria in their guts than kids without it; folks who have eczema live with different kinds of bugs on their skin than those who don't. As more and more people have their microbiomes mapped, scientists will be able to make more and more solid connections between specific bacteria and health conditions. "We're only just beginning to understand who's in there and what they're doing," says HMP investigator Barbara Methé, PhD.

Methé couldn't be more right. When I received my microbiome results, I was disappointed by the lack of information about the bugs milling around in my body. In fairness to uBiome, they simply didn't have many other samples to compare mine with yet. They were able to tell me what percentage of my bugs fell into four basic categories of bacteria, including firmicutes and proteobacteria. And based on what they know so far, the scientists concluded that my levels appeared to be within a healthy range. (High levels of firmicutes may point to an increase in a protein associated with inflammatory conditions like heart disease; lots of proteobacteria may be a sign of type 2 diabetes.)

What they couldn't tell me was how my levels of certain types of bacteria compared with those of people who are obese or have cancer—the stuff I really wanted to know. But these are exactly the sort of correlations researchers are starting to make. And that's where things get exciting.

Manipulating the Microbiome

We've long known that if your body's natural balance of bacteria is upset (whether by a course of antibiotics or an awful case of food poisoning), you can end up with diarrhea. But new research suggests that colon cancer, which kills about 50,000 people each year, could be another, more dire, outcome. Studies have found that patients with colorectal cancer have high levels of E. coli bacteria, the infamous fecal germs guilty of causing major outbreaks of food poisoning. While scientists are still studying the exact role bacteria play in the cancer's development (does an overgrowth of E. coli cause cancer? does cancer cause the overgrowth?), one thing's for sure: Increased levels of the bacteria signal trouble. The hope is that by monitoring bacteria levels in a person at risk of disease—in this case, colon cancer, but potentially diabetes, say, or rheumatoid arthritis—doctors will catch these conditions in their very early stages, and may be able to treat them simply by correcting the bacterial imbalance.

The same may be true for fighting obesity. In a study at New York University, children who had been given antibiotics before the age of 6 months were 22 percent more likely to become overweight preschoolers than kids who hadn't. In another study, rodents started packing on fat shortly after receiving antibiotics—gaining about 10 to 15 percent more than their unmedicated friends. Researchers believe the drugs altered the mix of bacteria, leading to a higher concentration of bugs that can extract more calories from food.

While scientists are still a long way from determining the perfect balance of bacteria for optimal health, one condition has been spectacularly responsive to microbiome intervention. Researchers in the Netherlands found that in people plagued by a bacterial infection that can cause potentially life-threatening diarrhea, fecal transplant—taking the feces of healthy people and introducing them into the guts of patients—led to a cure 94 percent of the time. By comparison, antibiotics worked on only 31 percent of patients. Doctors believe the "good" microbes in healthy poop take root in the sick person's body, where they restore the normal balance of bacteria and kill the dangerous bugs. Indeed, the treatment worked so well that the study was stopped and everyone who didn't respond to antibiotics was given a fecal transplant; all but four of the 42 patients were cured.

As unpleasant as the procedure may seem, its results highlight why the human microbiome has earned its place as a groundbreaking new frontier in medicine. "Unlike your genome, which is set from birth, your microbiome is very changeable," says Proctor. Just imagine a future in which we treat infections such as strep throat not with potent doses of antibiotics that wipe out both good and bad bacteria, but with a pill that fights off nasty germs by reseeding your body with helpful ones. "As we continue to unravel the role these microbes play within our bodies, we have the potential to open up a whole new avenue for wellness," Methé says.