Bacteria Do Not Add to Aging

Author:  Hoi See Tsao

Institution:  Wellesley College
Date:  August 2007

While it was once believed that harmless bacteria used up their host's energy by inducing an immune system response and increased the aging process, scientists from the University of Southern California have now shown that bacteria are actually not as bad as one may think.

The study, which appears in Cell Metabolism, showed that fruit flies that lived in a sterile environment had the same life expectancy as those kept in a non-sterile environment. Although the experiment cannot be reproduced in higher organisms due to the need for bacteria in digestion and other processes, the study may be relevant to research on human aging.

The number of bacteria living on both flies and humans increases proportionally with age. However, both organisms' innate immune responses to bacteria decrease with age. The study implies that factors such as our innate immune responses and the number of bacteria living on us are irrelevant to the aging process.

"I think a lot of people would just assume that if you're increasing bacterial load in an aging human, it must be bad," said lead researcher Dr. Steven Finkel.

The researchers compared three groups of flies. The control group consisted of normal fruit flies. The second group consisted of fruit flies born from eggs that were washed in antibiotics, raised in a bacteria-free environment and fed sterile food. The third group of fruit flies was initially raised with bacteria and was later disinfected upon maturation or reaching adulthood. The bacteria counts of the sterile group remained at zero while the bacteria counts in the other two groups increased with the age of the fly. However, the life expectancies of the flies in all three groups were approximately three months.

Finkel's colleague Dr. John Tower added, "Even though the flies were accumulating so much bacteria and a robust immune response to that bacteria, it's not limiting how long the flies live. The question is, if it's not bacteria that limit life span, then what is it?"

Written by Hoi See Tsao