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Interesting article from the NY Times on acne

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If the countless bacteria that dwell in and on the human body were cartoon characters, Propionibacterium acnes, a microbe that lives in the skin, might be a heavily armed superhero who doesn't know his own strength.

The bacterium is a major culprit behind acne vulgaris, otherwise known as pimples. It dwells in the hair follicles of every human being with a ferocity that surprises the scientists who have, for the first time, sequenced its genome.

The findings may lead to new treatments for acne, which affects four out of five adolescents worldwide, as well as many adults with chronic forms of the disease.

P. acnes has a circular chromosome with 2,333 genes, said Dr. Holger Brueggemann, a postdoctorate microbiologist at the Pasteur Institute in Paris and the lead author of a report, published in the July 30 issue of the journal Science, that describes the organism in painstaking detail.

The bacterium is a normal inhabitant of human skin, Dr. Brueggemann said, residing in follicles all over the body, although most commonly on the face, upper back and chest. Each follicle contains a tiny hair and several glands that produce an oily substance called sebum that is emptied onto the skin's surface. P. Acnes eats the oil.

Scientists believe that the bacterium helps produce acne when follicles becomes clogged.

Dr. Brueggemann and his colleagues report that the genome of P. acnes is not very large, but it is packed with functions that no one dreamed would be found in skin bacteria.

For example, it contains genes that secrete substances that kill competitors, like harmful bacteria and fungi, using the sort of weaponry usually seen in pathogens like tuberculosis and diphtheria. Unlike most bacteria, which choose a predictable niche, P. acnes can thrive with or without oxygen, switching easily between many types of environments. In laboratory dishes, it grows on just about anything, and it can also repair itself.

In terms of protecting the skin from dangerous microbes, the traits found in P. acnes make it a fierce warrior, Dr. Brueggemann said. And it may have as yet undiscovered defense strategies up its sleeve: a quarter of its genes have never been seen in any other organism.

On the other hand, P. acnes also has surprising destructive powers. The new genetic analysis shows that the bacterium has enzymes, similar to those seen in so called flesh-eating bacteria of the streptococcal strain, that destroy human tissue. These enzymes poke holes in cell membranes and help produce infection or tissue damage. P. acnes has five genes that make similar holes.

It also has genes that encode enzymes that degrade skin, producing waste products that serve as its own food supply. It other words, it breaks down skin and eats it, thus assuring its survival.

Dr. Brueggemann said the bacterium played a major role in inflammation. But it also has a strategy, called phase variation, that allows it to escape from attack by the human immune system. Such tricks allow P. acnes to adapt quickly to environmental change, he said.

While P. acnes is involved in a wide variety of diseases involving the cornea, heart, gallbladder, lung and other tissues, Dr. Brueggemann said its role in acne formation had been underestimated.

Dr. Linda Franks, an assistant clinical professor of dermatology at the New York University School of Medicine who treats many acne patients in her private practice, said chronic acne remained very difficult to treat. Current thinking is that P. acnes is not the primary cause, she said, but understanding its genome could change all that.

It is believed that acne begins when pores are plugged by bits of skin that become sticky instead of flaking away, Dr. Franks said. Oil collects behind the plugs and the bacteria thrive, setting up conditions for acne. Drugs containing vitamin A work by making skin shed more easily so the plugs don't build up.

On the other hand, the plugs may not be the primary cause of the disease, Dr. Franks said. Maybe it is the oil itself: more is produced during adolescence, and perhaps it is stickier in some people. Or acne could be caused by P. acnes bacteria interacting with other factors. When the microbe is trapped behind a pore, it goes into overdrive, guzzling excess oil. Components of the bacterium produce chemicals and enzymes that attract white blood cells that cause inflammation. When the wall of the plugged follicle breaks down, the contents are spilled onto nearby skin, where an acne lesion forms.

Treatments today are designed to prevent plug formation or kill bacteria, Dr. Franks said. But P. acnes has developed resistance to many of the antibiotics used for this purpose. Knowledge of the genes may lead to new, more effective targets.

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