Recent studies in rodents have found the bacteria do infect regions of the brain affected by Alzheimer's, that gum infections can worsen symptoms in mice genetically engineered to get Alzheimer's, and that gum infections can seemingly lead to brain inflammation and amyloid plaques in previously healthy mice.
Scientists at the company Cortexyme, working with academics from around the world, say the findings of their study could lead to new treatment options for Alzheimer's disease sufferers that work by targeting the bacterium Porphyromonas gingivalis, and they have developed a candidate drug that is now undergoing clinical trials.
"We now have strong evidence connecting P. gingivalis and Alzheimer's pathogenesis, but more research needs to be done before P. gingivalis is explicitly implicated in the causation or morbidity of Alzheimer's disease", said study co-author Jan Potempa.
A blood test would be able to test for the protein NfL, which may be associated with one of the genetic forms of Alzheimer's disease, and pick up the condition more than a decade before symptoms start to appear.
"Factors such as sleep might affect how fast the disease spreads through the brain", David Holtzman, senior author and neurology professor at Washington University School of Medicine said.
A large-scale clinical trial that will involve giving the drug to patients with mild to moderate Alzheimer's is planned for later this year.
While the patient groups had similar overall AD pathology, the authors found, Hispanics with AD showed greater small blood vessel disease in the brain than non-Hispanics with AD, as well as increased amyloid angiopathy, the accumulation of protein fragments in blood vessels associated with AD.
P. gingivalis infections are typically dealt with using antibiotics, but Dominy and his colleagues found that treating infected cells with antibiotics didn't stop the damage caused by the enzymes.
There was also caution about the fact the drug tests had been in mice.
The British Dental Association has used the news to remind the Department of Health on the importance of oral health. While evidence indicates PG can cause damage to brain cells, it is still unclear if this damage can result in Alzheimer's disease. "They did a lot of different experiments to build the case that gingipains are a drug target in Alzheimer's disease", he says. Since the study's publication, the neurologists are planning to expand their research to include more patients.
The findings, which were published in the January 14 issue of Nature Medicine, can potentially help with early Alzheimer's diagnoses and new drug development.
Many types of bacteria contributed to gum disease, but P. gingivalis was one of the most important. However, looking at the presence of bacteria in human brain tissue doesn't tell us anything about whether this may have a role in causing the disease.
"We collect blood, spinal fluid and urine to try and look for ... what people like to call biomarkers of Alzheimer's disease", said Michael Harrington, a director of neuroscience and research at HMRI.
"Everyone's life can be improved by regular appointments and good oral hygiene, reducing the bacterial load that's ever present in our mouths to a level that's unlikely to cause tooth decay, gum disease or tooth loss".