Microbes’ effect on health explored
WASHINGTON - Consider this: The average person’s body contains about 100 trillion cells, but only maybe 1 in 10 is human.
This isn’t the latest Hollywood horror flick, or some secret genetic engineering experiment run amok. The human cells that form our skin, eyes, ears, brain and every other part of our bodies are far outnumbered by those from microbes, primarily bacteria but also viruses, fungi, and other microorganisms.
This, it turns out, is nature’s way. A growing body of evidence indicates that the microbial ecosystems that have long populated our mouths, noses, intestines, and every other nook and cranny play crucial roles in keeping us healthy.
Moreover, researchers are becoming more convinced that modern trends - diet, antibiotics, obsession with cleanliness, Caesarean delivery of babies - are disrupting this delicate balance, contributing to some of the most perplexing ailments, including asthma, allergies, obesity, diabetes, autoimmune diseases, cancer, and perhaps even autism.
“In terms of potential for human health, I would place it with stem cells as one of the two most promising areas of research at the moment,’’ said Rob Knight of the University of Colorado. “Everywhere we look, microbes seem to be involved.’’
Equipped with super-fast new DNA decoders, scientists are accelerating the exploration of this realm at a molecular level, yielding provocative insights into how these microbial stowaways may wield far greater powers than previously appreciated in, paradoxically, making us human.
A five-year, $175 million study, the US Human Microbiome Project, is assembling an outline of a “healthy’’ microbiotic profile for humans by sampling the mouth, airway, skin, intestinal, and urogenital tract of 300 healthy adults, as well as deciphering the genetic codes of 200 possibly key microbes.
“The field has exploded,’’ said Jeffrey Gordon of Washington University, who pioneered the exploration of humanity’s microbial inhabitants, known as the “microbiome’’ or “microbiota.’’ “People have this sense of wonderment about looking at themselves as a compilation of microbial and human parts.’’
Some equate these microbial inhabitants to a newly recognized organ. Acquired at birth, this mass of fellow travelers may help steer normal development, molding immune systems and calibrating fundamental metabolic functions such as energy storage and consumption. There are even tantalizing clues they may help shape brain development, influencing behavior.
“The ‘human supraorganism’ is one term coined to describe the human host and all the attendant microorganisms,’’ said Lita Proctor, who leads the Human Microbiome Project at the National Institutes of Health, which is mapping this world. “There’s been a real revolution in thinking about what that means.’’
Investigators are trying to identify which organisms may truly be beneficial “probiotics’’ that people could take to help their health. Others are finding substances that people might ingest to nurture the good bugs. Drugs may mimic the helpful compounds that these organisms produce.
Doctors have even begun microbiota “transplants’’ to treat a host of illnesses, including a sometimes-devastating gastrointestinal infection called C. difficile, digestive system ailments such as Crohn’s disease, colitis, and irritable bowel disorder, and even in a handful of cases obesity and other afflictions, such as multiple sclerosis.
Many advocates of the research urge caution, noting that most of the work so far has involved laboratory animals or small numbers of patients, many hypotheses remain far from proven and nothing has zero risk.
“We have to be very careful in how we state what we know at the present time versus what we think might be true at this point,’’ said David Relman of Stanford University. “But it’s probably fair to say that our indigenous communities are more diverse, more complex, and more intimately and intricately involved in our biology than we thought.’’
Scientists have long known that many organisms evolved with humans and perform vital functions, digesting food, extracting crucial nutrients, and fighting off disease-causing entities.
But as microbiologists have begun scrutinizing these colonies, it has become clearer that they create carefully calibrated enterprises, with unique combinations inhabiting individual crevices and identifiable nuances from person to person.
European scientists reported in April that people generally seem to have one of three basic combinations that may be as fundamentally important as, say, blood type.
Dozens of studies are underway, including some that are repeatedly swabbing kids and adults, including twins, to gain insights into why one person gets tooth decay, asthma, ulcerative colitis, or even cancer, and another doesn’t.
One intriguing finding is that babies born through Caesarean sections apparently miss out on acquiring mothers’ microbiota.
“The birth canal is very heavily colonized by bacteria,’’ said Maria Dominguez-Bello, a University of Puerto Rico biologist who has been studying microbiota around the world, including in isolated tribes in the Amazon. “We think that is not by chance.’’