healthy bacteria

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A partial image of a New York Times graphic showing some microbes mapped by the Human Microbiome Project

Find out even more about the human microbiome and the relation between microbes and health in a second, more detailed article the New York Times published last week. Here’s a snippet.

In a study published last week in the journal PLoS One, Dr. Kjersti Aagaard-Tillery, an obstetrician at Baylor College of Medicine, and her colleagues described the vaginal microbiome in pregnant women. Before she started the study, Dr. Aagaard-Tillery expected this microbiome to be no different from that of women who weren’t pregnant.

“In fact, what we found is the exact opposite,” she said.

Early in the first trimester of pregnancy, she found, the diversity of vaginal bacteria changes significantly. Abundant species become rare, and vice versa.

One of the dominant species in the vagina of a pregnant woman, it turns out, is Lactobacillus johnsonii. It is usually found in the gut, where it produces enzymes that digest milk. It’s an odd species to find proliferating in the vagina, to say the least. Dr. Aagaard-Tillery speculates that changing conditions in the vagina encourage the bacteria to grow. During delivery, a baby will be coated by Lactobacillus johnsonii and ingest some of it. Dr. Aagaard-Tillery suggests that this inoculation prepares the infant to digest breast milk.

The baby’s microbiome continues to grow during breast-feeding. In a study of 16 lactating women published last year, Katherine M. Hunt of the University of Idaho and her colleagues reported that the women’s milk had up to 600 species of bacteria, as well as sugars called oligosaccharides that babies cannot digest. The sugars serve to nourish certain beneficial gut bacteria in the infants, the scientists said. The more the good bacteria thrive, the harder it is for harmful species to gain a foothold.

Plus: viruses and fungi may be in on the action; strongly worded quotes suggesting that antibiotics could disrupt healthy bacteria in unhealthy ways; and fecal transplants seem to be gaining approval and could be coming to you in pill form someday. Oh and there’s a sweet graphic.

Researchers suspect that, by harming healthy microflora in children, antibiotics can lead to asthma and allergies later in life. Microbes could also influence the weight of the mammals that host them—scientists have made thin mice obese by giving them the gut bacteria of other obese mice. So where do these obesity-causing bacteria come from? Probably a variety of places. Even the food you eat can change your microflora. According to the Economist, a study found that a sugary, fat-laden diet could change a child’s gut bacteria profile, leading to an increased risk of asthma, allergies and other inflammatory diseases. Food for thought.


An adult body carries four to five pounds of bacteria, and many of them are good bacteria that keep you healthy. Now scientists are trying to get a snapshot of what that healthy human microbiomes look like. If they succeed, we could get a deeper insight into how to live disease-free. The New York Times has an article on what they’re finding and how they’re doing it:

Researchers have taken a detailed look at … the 100 trillion good bacteria that live in or on the human body.

No one really knew much about them. They are essential for human life, needed to digest food, to synthesize certain vitamins, to form a barricade against disease-causing bacteria. But what do they look like in healthy people, and how much do they vary from person to person?

In a new five-year federal endeavor, the Human Microbiome Project, which has been compared to the Human Genome Project, 200 scientists at 80 institutions sequenced the genetic material of bacteria taken from nearly 250 healthy people.

They discovered more strains than they had ever imagined — as many as a thousand bacterial strains on each person. And each person’s collection of microbes, the microbiome, was different from the next person’s.

It sounds like this will be even more complicated than sequencing the human genome, but it will be a great baseline from which we can start to understand how all these microbes we carry around keep us alive.

I particularly like this bit:

Humans, said Dr. David Relman, a Stanford microbiologist, are like coral, “an assemblage of life-forms living together.”

Dr. Barnett Kramer, director of the division of cancer prevention at the National Cancer Institute, who was not involved with the research project, had another image. Humans, he said, in some sense are made mostly of microbes. From the standpoint of our microbiome, he added, “we may just serve as packaging.”

People are like planets, brought to life by all the critters living on them.

Here are two articles in Nature, one about the study and one about the diversity of the human microbiome.