Inside you right now there are more bacterial cells than human cells. In fact, if you cracked open every cell in your body, unwound the DNA, and stitched it together, you’d find ten to a hundred times more bacterial DNA than human DNA.

In our mouths, on our skin, and in our digestive and reproductive tracts, bacteria have been with us since the beginning, evolving with us. We know some of them. Researchers identified Lactobacillus acidophilus many years ago. You might know it from reading yogurt labels. It’s supposed to be good for us. E. coli live inside us. We know a lot about them. They’re not so good.

Most of the bacteria in our intestines, though, can’t survive exposure to oxygen, which means they can’t be cultured on a plate and studied like other bacteria. Scientists estimate that there are hundreds, maybe thousands, of species inside us, but we know little about them because we haven’t been able to study them—until now.

As part of the Human Microbiome Project, which is a National Institutes of Health mandate to identify and characterize the bacteria that call humans home, scientists use new methods that allow them to isolate and sequence bacterial DNA. This means they are finally identifying more strains of bacteria. At UNC, some of these new technologies are housed in the Microbiome Core Facility, where researchers can figure out the bacterial composition of, well, anything. And there are plenty of reasons why we want to figure out what bacteria are doing inside of us, especially in our bellies.

For centuries scientists didn’t think our relationship with bacteria was terribly important, except in those rare cases when bugs escape the GI tract, enter the bloodstream, and cause a life-threatening infection. Then researchers started figuring out that our intestines are full of known and unknown species that compose unique bacterial ecologies. And each of us, they’re finding, has a symbiotic relationship with these bacteria.

Today we’re learning that diverse groups of bacteria play major roles in several ailments, including colitis, Crohn’s disease, irritable bowel syndrome, obesity, diabetes, cystic fibrosis, and even colon cancer. Scientists at Carolina and elsewhere are proving that probiotics—the so-called good bacteria sold at health-food stores—can help millions of people, including kids. And they’ve found that bacteria’s effect on health starts when we’re babies.

In five stories, UNC researchers tell of their findings even as they continue to explore uncharted territory—inside us.

Bacteria in your body

On the attack
What triggers the inflammation that causes gut problems?

The "good" bugs
And why you want them

The battle for baby's belly
Not all newborns have the same bacterial compositions.

Big, bad bacteria
Are gut microbes implicated in the worst kind of colon disease?

Bugs in the lungs
More than a lone gunman


cartoons by Eric Knisley