We cannot survive without bacteria. They provide immune stimulation.

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Our friend the bacterium

Recent bad press for microbes shouldn't obscure that, sometimes, germs are good

for us.

By Zuk

MARLENE ZUK's book " Riddled with Life: Friendly Worms, Ladybug Sex and the

Parasites That Make Us Who We Are " is due out in April. She is a professor of

biology at UC Riverside.

February 10, 2007

WE ALL KNOW that bacteria and other microbes can make us sick. Now, it turns

out, they might also make us fat. Recent research comparing the " gut flora " of

overweight and slender mice — as well as people — showed that the microorganism

count varied consistently in the two groups. Plump individuals have more of one

kind, leaner types have more of another. The cause-and-effect relationship, if

one exists, is not at all clear. Maybe the bacteria are an indicator of fatness

but not its cause (like owning a lot of elastic-waist pants), or maybe having

those microbes means obese people metabolize food differently than lean people,

giving them distressingly more bang for their caloric buck.

Either way, these findings don't do much to improve the reputation of microbes.

Just saying " bacteria " and " fat " in the same sentence is enough to reinforce a

million toothpaste commercials: Bacteria are bad. . In fact, humans and microbes

have a deep, seamless relationship — for good and ill, but mostly for good.

For starters, we are not just occasionally dusted or doused in bacteria; we

wallow in them, with more than 2,000 different kinds swarming in our insides, on

our skin and hair, inside our noses and mouths. Most cause us no harm — fewer

than 100 types of bacteria cause disease — and rather than fighting them off

tooth and nail, we can wallow at will.

The key research isn't about fat or even E. coli but basic health. Exposure to

bacteria appears to calibrate our immune systems to distinguish harmless (or

beneficial) co-inhabitants of the planet from threatening pathogens.

Scientists are increasingly convinced that the lack of " immune stimulation " — a

lack of exposure to microbes — in childhood can cause problems with allergies

and asthma later in life, turning innocuous substances such as pollen or peanuts

into deadly killers.

The need for immune stimulation starts early. A group of Norwegian researchers

looked for a connection between children's sensitivities to eggs, fish or nuts

and whether they had been born vaginally or via cesarean section.

Childbirth, in case you hadn't noticed, is a rather messy process, and along

with an introduction to air, light and exclamations of joy, a newborn receives a

hearty dose of bacteria to colonize his or her intestinal tract during the

passage through the birth canal. Babies removed surgically from their mothers

miss out on this germ-laden opportunity; they acquire their intestinal menagerie

more slowly than vaginally delivered children.

The research found that when a mother was allergic to eggs, fish or nuts, her

child was seven times more likely to share that allergy if he or she had been

born by C-section.

Other work has found that exposure to microorganisms via pets, siblings and a

rural lifestyle can mean a lower incidence of allergies and asthma in older

children. Such ailments are much more rare in less-developed countries, even

when pollution levels are high. And although parents may fret about colds their

children catch in day care, having more colds as a youngster seems to mean less

asthma later in life. This is not to say that sickness is good but that a life

without microbes — even the ones that cause disease — can cause more problems

than it solves.

Other research indicates even deeper connections between our health and our

microbes. Margaret McFall-Ngai of the University of Wisconsin suggests that the

complex immune system of vertebrates, including humans, may owe its ability to

remember previous encounters with diseases — and therefore trigger antibodies to

fight them — to the need for dealing with the vast array of microbes we live

with. She theorizes that such " memory " is important primarily in developing a

way to manage the masses of microbes that can inhabit our bodies and that the

immune benefits are just gravy.

The moral of the story is that our bodies and our lives are so enmeshed with

microbes that it's futile, and potentially even harmful, to try to get rid of

them with soaps and wipes and purifiers. So get over all those scare stories

about the number of bacteria on your telephone or toilet seat. They belong

there, for the most part, and you would miss them if they were gone.

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