OF MICROBES AND MEN
feeling quite yourself?
wonder. In a sense, you aren't really you.
estimate that 90 percent of the cells contained in the human
body belong to nonhuman organisms - mostly bacteria, but also
a smattering of fungi and other eensy entities. Some 100 trillion
microbes nestle in niches from our teeth to our toes.
what's setting science on its heels these days is not the boggling
numbers of bugs so much as the budding recognition that they
are much more than casual hitchhikers capable of causing disease.
They may be so essential to well-being that humans couldn't
live without them.
this emerging view, humans and their microbes -- or, as some
biologists playfully put it, microbes and their attached humans
-- have evolved together to form an extraordinarily complex
not individuals, we're colonies of creatures," said Bruce
Birren, director of microbial sequencing at the Broad Institute,
a research center affiliated with Harvard and the Massachusetts
Institute of Technology. His team is part of a newly launched
effort by the US National Institutes of Health to map the DNA
and complete the first comprehensive census of microbial species
that are inseparable from human existence.
can't take nutrition properly without bacteria. We can't fight
bad germs without good germs," he said. "It may turn
out that secretions from bacteria affect not only long-term
health, but hour-by-hour moods - could a person's happiness
depend on his or her bugs? It's possible. Our existences are
so incredibly intertwined."
in the opinion of some researchers, this strange union may be
headed for trouble because of profligate use of antibiotics
and antiseptic lifestyles that deter the transfer of vital strains
of bacteria that have swarmed in our systems at least since
early humans ventured out of Africa.
strains of bacteria are disappearing from humans, especially
in industrialized countries, and may be linked to germ-destroying
substances in everything from hankies to hamburger.
seeing the equivalent of global warming in the human ecosystem,"
said Dr. Martin J. Blaser, professor of microbiology and chairman
of the department of medicine at New York University. "Changes
of huge magnitude are occurring over a few generations. Nature
famously abhors a vacuum -- the bacteria disappearing from our
systems ... might be replaced by organisms that aren't nearly
the late 19th century, when microbes were discovered, researchers
have focused mostly on bacteria that cause disease.
one was paying too much attention to the vastly more numerous
species [within the body] that do no harm and may be doing a
great deal of good," said Roberto Kolter, professor of
microbiology at Harvard Medical School and president-elect of
the American Society of Microbiology. "Without these microbes,
human beings would be in trouble."
human gut, throat, mouth, skin, and other anatomical regions
host thousands of species of microbes that have never been tallied,
much less scrutinized. The bacteria and other microbial entities
are tiny, so while they make up the huge majority of cells living
on and within us, they are just a fraction of our overall bulk.
the human genome was completed in 2003, scientists were stunned
to realize that humans possessed only about 20,000 genes, far
fewer than expected. In contrast, microbiologists estimate the
microbes in our systems carry 3 million genes, with which we
constantly exchange molecular substances involved in growth,
development, and reproduction.
emerging theories, human development and behaviour -- as well
as health -- may be influenced by the genes of the species within.
"We haven't got the hard evidence, but that's where the
science is headed," said Kolter.
new thinking grew partly from 1990 work by Norman Pace, a University
of Colorado professor who used DNA analysis to show more biodiversity
in an ounce of sediment from hot springs at Yellowstone National
Park than scientists had previously suspected existed in the
entire world. That inspired microbiologists to begin seeking
DNA in all sorts of odd places - leading to discoveries that
multiple species of bacteria thrive in areas, like the esophagus,
long assumed inhospitable to life.
recent years, microbial science has been hindered by the fact
that many strains of bacteria cannot be "cultured,"
or coaxed to reproduce in Petri dishes in the lab. That made
them difficult to study using the time-honoured tools of microscope
now high-powered and relatively inexpensive DNA sequencing technology
similar to that used to map the human genome is being turned
on our microbes. A five-year Human Microbiome Project underway
since last month will seek to turn a genetic spotlight on the
thousands of species that pervade five regions of the anatomy
- the digestive system, mouth, nose, skin, and female urogenital
goal is to discover what microbial communities exist in different
parts of the body and how these communities affect health and
disease," said Lu Wang, program director for large scale
sequencing at the National Human Genome Research Institute.
all of the body is infused with germs. The brain, blood system,
and most organs appear to be microbe-free, say scientists.
are born kicking, screaming -- and sterile. The womb contains
no germs, but the moment a new baby emerges it is colonized
by rapidly multiplying microbes - from its mother's breast,
from the clothes in which it is first swaddled, from the germ-imbued
air of its first breath.
every baby acquires the same germs. A baby born by Caesarean
section, for example, will pick up other germs than a baby delivered
through the birth canal. And there are hints that acquiring
the right combination of bacteria affects health in ways similar
to inheriting good genes.
the composition of the microbial swarms within humans varies
in different parts of the world, some germs seem to have accompanied
humans everywhere, and the waning presence of some of these
bugs within inhabitants of the industrialized world is cause
for puzzlement among researchers - and some alarm.
the stomach bacterium Helicobacter pylori, an ambivalent germ:
It has been linked to ulcers and stomach cancers. But it also
may guard against asthma and diseases of the esophagus, according
to new research.
Africa, 90 percent of children carry h. pylori in their stomachs.
So did children in the United States, until a few decades ago.
bacteria seem to be transferred within families who live in
close proximity, sharing beds, eating utensils, and tight quarters.
These days, only about 5 percent of American children harbour
the bacteria -- that's because US kids often grow up in small
families, occupy private bedrooms, drink clean water, and scarf
food from plates scoured in dishwashers using antibacterial
good consequence is that stomach disease is on the decline in
the West, say researchers.
diseases of the esophagus, allergies, and childhood asthma are
on the rise. And research by Blaser and NYU epidemiologist Yu
Chen suggests that h. pylori provided protection against esophageal
diseases -- including cancer -- as well as asthma. Their study
last year of 7,663 adults found that those who carried the bacteria
were 40 percent less likely to have had asthma under age 15
than those who didn't host it.
we see, for certain, is that human micro-ecology is changing
right under our noses," said Blaser. "This bacterium
has been the dominant organism in our stomach for tens of thousands
of years. Now it's disappearing. I suspect if [h. pylori] was
totally bad for us, it wouldn't have been there. So I think
the disappearance will have consequences. You can compare this
to changes occurring in the world environment - species that
may be vital are vanishing too fast."
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article originally appeared in ©
The Boston Globe.