Why Millions of Bacteria on You Right Now Is a Good Thing

December 12th, 2016

By Gary Evans, Medical Writer

Multidrug-resistant bacteria have emerged in such overwhelming numbers that we are painfully reminded that the miracle of antibiotics in medicine is less than a century old -- a nanosecond in the immense time span microbes have ruled the earth.

But amid the legitimate warnings of infections that could be both untreatable and unpreventable, one truth should not be lost: not all bugs are bad. In fact millions of bacteria play a vital role in protecting us from disease.

According to the National Institutes of Health, the human microbiome is the collection of all the microorganisms living in association with the human body.

“Bacteria in an average human body number ten times more than human cells, for a total of about 1000 more genes than are present in the human genome,” the NIH notes. To put that in perspective, the NIH estimates that that microorganisms comprise 1% to 3% of our body mass – two to six pounds in a 200-pound adult.

“The metaphor of a ‘war’ against bacteria is really misleading,” says Tom Frieden, MD, director of the Centers for Disease Control & Prevention. “If you look at the microbiome, our 23,000 or so genes are up against 1 million or so bacteria that call each of our bodies home. Until a few months ago, around 80% of the bacteria in our intestines had never been cultured, though we knew they were there from [genetic] sequencing. We don’t have to go to the bottom of the ocean or to Mars to look for unusual bacteria. They are within us.”

These commensal bacteria have some known benefits, but for the most part are an undiscovered country, a colony if you will, within and without the human body.

“They may contain within them important messages on what maintains health and what can be used to control infections,” Frieden says. “There are many more friendly bacteria around than there are unfriendly ones, and we disrupt them at our peril. The dictum of ‘above all do no harm’ also relates to the microbiome. We are just beginning to scratch the surface of what we need to know to do that.”

Indeed, the microbiome of commensal bacteria may function in some sense as a “separate organ” in the body. Thus, the old-school approach of carpet bombing the gut with antibiotics has been shown to set up pathogens like Clostridium difficile by killing off our commensal bacteria that comprise our microbiome.

“It may protect us,” Frieden said. “It may have metabolic functions. It may help us with digestion. There are a lot of things that the healthy microbiome does. When we use antibiotics, we wipe out the good with the bad and we leave behind a system that doesn’t have the usual protectors. Because of the relative absence of our friendly bacteria the body becomes susceptible to infection and resistant bacteria can thrive in that disrupted microbial environment.”

For more on this story see the January 2017 issue of Hospital Infection Control

Gary Evans has written about infectious diseases, occupational health, medical ethics and a variety of other healthcare issues for more than 25 years. His writing and has been honored with five awards for interpretative and analytical reporting by the National Press Club in Washington, DC.