Only a stomach that rarely feels hungry scorns common things - Horace


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You probably know the human body hosts a variety of microbes, but you might be surprised by the volume.

If the collection of bacteria, fungi and other organisms could be shed all at once, it would weigh 2 to 4 pounds and fill one or two quarts.

En masse, scientists call it the microbiome and have come to believe it is as important to good health as a sound brain, heart, kidneys, liver and lungs.

It helps digest our food, regulate our immune system and feed the cells that line the gut. But if its mix of microbes gets out of whack, the same organisms that ensure our health can make us sick.

“Not only irritable bowel syndrome and inflammatory bowel disease, but cardiovascular disease, even Parkinson’s, autism and multiple sclerosis,” said Rob Knight, director of the Center for Microbiome Innovation at the University of California in San Diego.

Remarkably, those illnesses—as well as obesity—have been transferred to mice by implanting the rodents with samples of the microbiomes of humans who suffer from the disorders.

“You can take a condition that affects the nervous system or brain and transmit it across species with the microbiome,” Dr. Knight said. “It’s pretty amazing.”

Although there is still much to learn, there is hope that in the future researchers will be able to use the microbiome to treat diseases.

In one small study, for example, fecal transplants introduced to rebalance the microbes of the gut improved symptoms of autism. And in controlled studies, researchers can distinguish healthy individuals from those who are sick by examining their microbiomes.

“If you have certain microbes, we don’t know if you are more likely to get a disease or, if when you get a disease, it changes your microbes,” Dr. Knight said. “What you want to know is can your microbiome predict interventions that will work.”

The first step in understanding the microbiome is to document the assembly of microbes, and each person’s appears to be unique.

The American Gut Project has collected more than 15,000 microbiome samples, and none are identical. That doesn’t rule out the possibility of doppelgängers among the 7.6 billion people who inhabit the Earth, but it’s possible that, in addition to medical therapies, the microbiome could be useful as trace evidence in criminal investigations, just like fingerprints or DNA.

The microbiome occupies the skin and the body’s various orifices, but it is primarily composed of bacteria that reside in the gut, a constantly changing environment.

“The gut contents are thick except when you empty your bowels,” said Maria Gloria Dominguez-Bello, a professor of microbiome and health at Rutgers. “Then, suddenly, it’s reduced.”

Still, estimates of the weight and volume of the microbiome are based on what researchers are able extract from the gut.

“It’s like taking a biopsy,” Dr. Knight said. “You suck out the gut content, get rid of the water and with the mass you have left, you figure out the number of human and other cells.”

After discerning the proportion of bacteria in the sample, researchers capture the total volume of the of the gut content by CT or MRI and extrapolate the full size of the microbiome.

Another way of thinking of its size is as a ratio to the number of human cells in the body. An often repeated but disputed number suggests there are 10 microbes for every human cell.

Researchers at the Weizmann Institute of Science in Israel recently revised the ratio to one-to-one but even that estimate is debatable because of choices about which human cells to count (are nonnucleated red blood cells in or out?) as well as individual microbial differences.

Not all of the organisms in the human microbiome have been identified, but one of the better known is E. coli, a sometimes deadly bacteria that provided early evidence that microbes could be beneficial in treating human disease.

In World War I, a special kind of E. coli was found in a German soldier who, unlike his comrades, didn’t develop infectious diarrhea while stationed in an area of Europe where the disease was endemic.

E. coli Nissle, named for the professor who isolated the strain in 1917, became the active ingredient in a drug used to treat diarrhea, ulcerative colitis and other gastrointestinal disorders.

While there is no doubt that reducing pathogens has improved public health, scientists now suspect that in our zeal to avoid infection, we may have separated ourselves from some benefits of bacteria.

“There is increasing evidence that exposure to healthy microbes in the earth, dust, air and water and on pets may be good for us,” Dr. Knight said.

It’s a whole new way of thinking about germs. But, please, do wash your hands.

Source: Jo Craven McGinty, Gut Feeling: To Stay Healthy, Keep Your Body’s Microbes in Line, The Wall Street Journal, August 17, 2018.

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Last Updated : Sunday, June 9, 2019