LOS ANGELES (AP) - Infection of a person's brain cells by a type of bacteria commonly found in the sinuses and lungs may raise the risk of Alzheimer's disease late in life, researchers suggested Wednesday.

Scientists who examined brain tissue of Alzheimer's patients after they died found a bacterium called Chlamydia pneumoniae had gotten into cells in regions where Alzheimer's damage is detected.

The presence of the bacterium was unexpected, because it meant the germ had to penetrate the protective blood-brain barrier.

Brian J. Balin, a researcher at Allegheny University of the Health Sciences in Philadelphia, presented the findings at a meeting in Los Angeles of the Society for Neuroscience.

A top Alzheimer's expert called the findings exciting.

``I think that it's something that's really worth taking seriously because of the issue of what's triggering the degeneration process,'' said Zaven Khachaturian, a consultant to the Alzheimer's Association and former director of the Office of Alzheimer's Disease Research at the National Institutes of Health in Washington.

Khachaturian said it will be important to find out whether the bacteria set the stage for Alzheimer's, or whether Alzheimer's damaged the brain and let the bacteria in.

Balin's team found segments of the bacterium's DNA in brain samples of 17 of the 19 Alzheimer's patients he analyzed. Conversely, 18 of 19 brain samples from people without Alzheimer's showed no signs of the organism.

Cells infected by the bacterium make chemicals to fend off the infection. Those inflammatory chemicals, called cytokines, can in turn damage surrounding nerve cells.

The same bacterium has been detected in the fatty plaques that clog heart arteries, though researchers do not yet know if it is responsible for the clogging.

Researchers have also found a correlation between late-onset Alzheimer's and infection with herpes simplex virus type 1.

Copyright 1998 The Associated Press. All rights reserved.

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