90% of our Body is Not Us

[Guest guest]

http://discovermagazine.com/2007/jun/your-body-is-a-planet

" We may not realize it, but each one of us is a walking ecosystem...

Most of the time we share our bodies harmoniously with the 90

trillion or so microbes. " [see the Web site for the photos that go

with each of the 10 points].

Carl Grimes

Healthy Habitats LLC

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Your Body Is a Planet

06.19.2007

Discover

90% of the cells within us are not ours but microbes'.

by Josie Glausiusz

We may not realize it, but each one of us is a walking ecosystem.

Minuscule, eight-legged Demodex mites nestle head down inside the

follicles of the eyelashes, feasting unnoticed on skin cells.

Microscopic yeasts live on the tongue, teeth, and skin and in the

intestine. Dormant viruses like herpes simplex may loiter for years

inside nerve cells. Perhaps strangest of all are the self-

replicating, viruslike pieces of DNA that infected ancient humans and

still make up about 8 percent of our genome.

Most of the time we share our bodies harmoniously with the 90

trillion or so microbes. But sometimes the arrangement turns

contentious, as when blood-sucking bedbugs, fleas, and lice invade,

or when herpes simplex or human papillomaviruses cause surface

membranes to erupt in nasty pustules or warts. Just taking

antibiotics may disturb the ecosystem in our gut by killing not only

disease-­causing organisms but also good bacteria, like Lactobacillus

acidophilus.

Living with microbes demands a biological balancing act. For the most

part, though, we are blissfully oblivious to the microscopic life we

carry around with us. Considering what those organisms look like,

that may be a good thing.

1 Athlete´s foot fungus Trichophyton and Epidermophyton are

filamentous, parasitic microbes that latch onto bare feet in communal

showers. These species and their relatives can creep under the

toenails and invade other areas of the skin, including the scalp and

genitalia, where they trigger ringworm and jock itch.

2 Vaginal flora Beneficial bacteria-notably members of the

Lactobacillus family-inhabit the vagina, secreting lactic acid and

fending off hostile invaders like the pathogenic yeast Candida

albicans.

3 Firmicutes and Bacteroides At least 500 species of bacteria,

weighing about 3.3 pounds, live inside the human gut. The majority

are from one of two phyla, the Firmicutes and the Bacteroides. They

break down carbohydrates and make essential nutrients like vitamins K

and B12. They also crowd out harmful bacteria. As Sears at

s Hopkins Center for Global Health says, " Just by mere force of

numbers, the bad bugs are beat out by the good bugs. "

4 Human papillomavirus More than 100 types of human papillomavirus

(HPV) can infect humans, causing a variety of warts from the common

wart to plantar and flat warts. At least 30 strains of HPV are

sexually transmitted, and the CDC estimates that at least 50 percent

of sexually active men and women will be infected with genital HPV at

some point. Of greatest concern are HPV types 16 and 18, which can

cause cancers of the cervix, penis, vagina, anus, and rectum. The new

vaccine Gardasil protects against the cancers caused by both HPV

types.

5 Head lice Pediculus humanus capitis (the head louse) has been

around for a long time: One ancient louse egg has been found attached

to a strand of hair 10,000 years old. The flat, wingless insects are

tiny (between one and two millimeters long-less than a tenth of an

inch), suck on human blood, and cement their eggs, or nits, to our

hair.

6 Dental streptococcus If you don't brush regularly, you probably

have a biofilm of bacteria 300 to 500 cells thick on the surface of

your teeth. The dominant species in this dental plaque are

Streptococcus sanguis and S. mutans. Even if you brush diligently,

these bacteria will still be there: They arrive soon after your teeth

do and stay until they fall out. The bacteria ferment sugars and

secrete gluey polymers that form the basis of plaque.

7 Demodex mites A little arthropod most likely lives in the

follicles of your eyelashes, eating, mating, breeding, and rarely

leaving-except perhaps for a sporadic nighttime walk around your

face. Demodex mites-cigar-shaped, stumpy-legged parasites about 0.3

millimeter long-infest about 20 percent of people under 20. They are

more likely to infect us as we age, so nearly all elderly people

carry them.

8 Shingles Once you have had chicken pox, the virus, called

varicella-zoster, stays inside you forever, lying dormant in nerves

near the spinal cord. Stress, aging, or a weakened immune system may

reactivate the virus, which can then slink along nerve tracts,

causing persistent pain and nasty skin rashes-a condition known as

shingles. Research suggests that widespread vaccination against

chicken pox, now common in the United States, may lead to a

significant increase in shingles among the elderly.

9 Fossil viruses About 1/12 of our genome consists of stretches of

DNA from viruses that infected our ancestors millions of years ago.

According to epidemiologist Prescott Deininger of Tulane University,

these and other parasitical, self-replicating pieces of DNA have

evolved with us and can insert copies of themselves into our genome,

leading to mutations that may cause new genetic diseases.

10 Staphylococcus On average, the skin supports about 1 trillion

bacteria. The most common include staph, Streptococcus, and

Corynebacterium, which metabolize sweat to produce body odor.

Microbiologist Blaser of the New York University School of

Medicine sequenced the DNA of bacteria from the forearms of six

people and discovered 182 separate species of bacteria. Most of those

bacteria actually help to keep the skin healthy by competing with

dangerous pathogens for nutrients. As Blaser explains, " I would hate

to live without them. "

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