How to Live Long and Prosper: Get Dirty?

Germs go both ways, helping our health at times and killing us at others. A new study suggests they might give the gift of a long life, at least to fruit flies.

Early exposure to bacteria makes these banana-peel denizens live to the ripe age of about three months, according to a recent paper in Proceedings of the National Academy of Science.

For a fruit fly, that's 30 percent longer than usual.

"In short, what we find is bacteria are good for young flies," said biologist Ted Brummel, who was in charge of the research project while at Caltech but is now at Sam Houston State University.

The "dirty living" effect worked only in the first week of life. In mid-life, exposure to bacteria had no effect. And later in life, it shortened life.

Does this mean we should cut back on infants' baths and house grandparents in glass bubbles to live as long as Methuselah? It's not that simple.

Before birth (or hatching,) fruit flies, like humans and most other animals, develop in a germ-free environment. After birth, numerous strains of bacteria set up house over time in animals' bodies.

The longevity effect of bacteria among creatures varies. Parameciums and termites grown in sterile environments age more rapidly. For a worm called C. elegans and for mosquitoes, such clean living harms their development but lengthens their lives.

In recent years, scientists have shown that bacteria in humans influence ulcers, cancer, appetite, and gut development. Certain bugs also duke it out with other bugs in our bodies, keeping us disease free.

To tease out a simpler case, the Caltech team studied the give and take between bacteria and fruit flies across their lifespan. The experiment involved raising flies in germ-free test tubes and then controlling the timing of flies' exposure to bacteria using antibiotics in their food. The results showed the early time window was important. Even if flies only lived with germs in their first week of life and then were given antibiotic-treated food for the rest of their lives, they lived longer than those raised in total sterility.

As for humans, some scientists say that early exposure to "dirt" might explain the lower incidence of allergies in the developing world.

The experiments also underscore the ongoing concern among health care experts about the routine use of antibiotics. Early use of antibiotics in humans has been linked to asthma. And over-use of antibiotics has resulted in drug-resistant strains of tuberculosis, salmonella, bacteria that cause pneumonia, and many others.

For now, scientists hope that more knowledge of the workings of bacteria and longevity in fruit flies will help them design experiments to see if the same exposure and timing mechanisms apply in humans. The mass of all the planet's bacteria and "archaea" cousins (both types of these single-cell organisms lack a central nucleus) weighs as much as all the plants on Earth. Most of them live under land or the sea floor, although a fair number of them live in the human gut.

"The truth is," Brummel said, "we really know very little about most of the species of bacteria living within our bodies and how they affect our fitness."