E. coli, salmonella could cause
Alzheimer's, study suggests
By André Picard
PUBLIC HEALTH REPORTER
Friday, February 1, 2002 – Print Edition, Page A3, Globe and Mail
Common bacteria such as E. coli and salmonella produce tangled fibres identical to those found in the brains of people with Alzheimer's disease, a new study says.
The research, published in Science, provides startling evidence that organisms that cause food poisoning and urinary tract infections may be responsible, at least in part, for devastating neurological diseases later in life.
The finding also gives scientists an easy way to study how these so-called amyloid fibres grow, which could lead to the development of drugs that block their production in the human brain.
In people, amyloid fibres can accumulate in the brain, forming a gooey plaque that slowly kills off the cells, as in Alzheimer's and Creutzfeldt-Jakob disease. The production of amyloid has long been seen as a biological error.
But bacteria produce these fibres purposefully, said Dr. Scott Hultgren, a molecular biologist at Washington University in St. Louis and lead author of the study.
"This is the first example of dedicated molecular machinery to produce amyloid and thus shows that amyloid production is not always a mistake," he said. In fact, the fibres form a mesh around bacteria, making them more resistant to antibiotics and to the body's immune system.
Dr. Matthew Chapman, another molecular biologist involved in the study, said the fibres form in the same way ice crystals gather to create a snowflake.
The big question is what triggers the process that leads to the dangerous buildup of plaque in the brain. The researchers speculate that bacterial infections could play a role in the development of amyloid plaque in at least two ways: Bacteria might produce the fibres directly, or their presence might cause proteins already in the body to begin producing them.
Either way, it suggests that eating undercooked food or drinking unclean water could have farther-reaching and more lasting effects than scientists had imagined.
But it also carries with it the faint promise that devastating illnesses such as Alzheimer's may be preventable, perhaps even with the judicious use of antibiotics.
"Learning that bacteria produce amyloid is a revelation," said Paul Berg, a professor emeritus at Stanford University School of Medicine and winner of the 1980 Nobel Prize in chemistry.
He said researchers will now be able to take bacteria such as E. coli and salmonella and study the molecular details of amyloid formation. That will go a long way toward explaining how the process occurs in humans, Dr. Berg said.
In the new research, scientists looked at several strains of the bacterium Escherichia coli, but they did not look specifically at E. coli 0157:H7, the deadly strain that infected the water supply in Walkerton, Ont.