Caution: Killing Germs May Be Hazardous to Your
Our war on microbes has toughened them. Now, new science tells us we should
Jerry Adler and Jeneen Interlandi
From the magazine issue dated Oct 29, 2007
Behold yourself, for a moment, as an organism. A trillion cells stuck together, arrayed into tissues and
organs and harnessed by your DNA to the elemental goals of survival and propagation. But is that all?
An electron microscope would reveal that you are teeming with other life-forms. Any part of your
body that comes into contact with the outside world—your skin, mouth, nose and (especially) digestive
tract—is home to bacteria, fungi and protozoa that outnumber the cells you call your own by 10, or
perhaps a hundred, to one.
Their ancestors began colonizing you the moment you came into the world, inches from the least
sanitary part of your mother's body, and their descendants will have their final feast on your corpse,
and join you in death. There are thousands of different species, found in combinations "as unique as
our DNA or our fingerprints," says Stanford biologist David Relman, who is investigating the complex
web of interactions microbes maintain with our digestive, immune and nervous systems. Where do you
leave off, and they begin? Microbes, Relman holds, are "a part of who we are."
Relman is a leader in rethinking our relationship to bacteria, which for most of the last century was
dominated by the paradigm of Total Warfare. "It's awful the way we treat our microbes," he says, not
intending a joke; "people still think the only good microbe is a dead one." We try to kill them off with
antibiotics and hand sanitizers. But bacteria never surrender; if there were one salmonella left in the
world, doubling every 30 minutes, it would take less than a week to give everyone alive diarrhea. In
the early years of antibiotics, doctors dreamed of eliminating infectious disease. Instead, a new paper
in The Journal of the American Medical Association reports on the prevalence of Methicillinresistant
Staphylococcus aureus (MRSA), which was responsible for almost 19,000 deaths in the United States
in 2005—about twice as many as previously thought, and more than AIDS. Elizabeth Bancroft, a
leading epidemiologist, called this finding "astounding."
As antibiotics lose their effectiveness, researchers are returning to an idea that dates back to Pasteur,
that the body's natural microbial flora aren't just an incidental fact of our biology, but crucial
components of our health, intimate companions on an evolutionary journey that began millions of
years ago. The science writer Jessica Snyder Sachs summarizes this view in four words in the title of
her ground-breaking new book: "Good Germs, Bad Germs." Our microbes do us the favor of
synthesizing vitamins right in our guts; they regulate our immune systems and even our serotonin
levels: germs, it seems, can make us happy. They influence how we digest our food, how much we eat