Common respiratory bacteria detected in eyes of Alzheimer’s patients

A bacterium prevalent in sinus infections and pneumonia may aggravate Alzheimer’s disease, according to a recent study published in Nature Communications. 

The bacterium, Chlamydia pneumoniae, was found in the eyes of deceased patients with Alzheimer’s disease, according to researchers from Cedars-Sinai’s Health Sciences University in California.

"The retina is directly connected with the brain. It's a developmental extension of the brain," lead researcher Maya Koronyo-Hamaoui, PhD, professor of neurosurgery, neurology and biomedical sciences at Cedars-Sinai Health Sciences University, told Fox News Digital.

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The study showed that Chlamydia pneumoniae could reach the retinal tissue that lines the back of the eye and linger for several years, creating an inflammatory response potentially linked to the death of nerve cells. This could contribute to cognitive decline and could worsen Alzheimer’s disease symptoms. 

The findings point to potential therapies for Alzheimer’s disease that would target inflammation and provide antibiotic treatment in the early stages of infection, according to Koronyo-Hamaoui.

"One hope of this study is that when people do present with some [symptoms of] pneumonia or atypical pneumonia or some respiratory infection, doctors should consider testing specifically for Chlamydia pneumoniae, and then give them the specific antibiotic," the researcher said.

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The infection can be identified through laboratory testing, including PCR (polymerase chain reaction), blood tests, or cultures that allow live organisms to grow for analysis.

The researchers examined retinal tissue samples from over 100 deceased individuals who fell into three groups: those who had Alzheimer’s disease, those who had some cognitive deficit or those who did not have the disease. 

They analyzed proteins, conducted genetic testing and used advanced imaging techniques on the samples. Those with Alzheimer’s disease had higher levels of the bacterium in their brains and retinal tissue compared to those who had normal cognition, the release stated.

Higher levels of chlamydia pneumonia were found in those who carried the gene variant APOE4, which is an associated risk factor for Alzheimer’s disease, Koronyo-Hamaoui added. The bacterium was also associated with more severe cognition decline.  

The Cedars-Sinai team also looked at human neurons and lab mice with Alzheimer’s disease, finding that Chlamydia pneumoniae was linked to increased inflammation, nerve cell death and cognitive decline, further suggesting that it may play a role in accelerating the disease. 

The infection also prompted production of amyloid-beta, which is a protein known to accumulate in the brains of those with Alzheimer’s, Koronyo-Hamaoui said.

While the study points toward using the retina as a way to diagnose and monitor the disease, the researcher acknowledged that more research is needed to confirm these findings.

Dr. Aaron Glatt, chief of infectious diseases at Mount Sinai South Nassau on Long Island, New York, was not involved with the study but called the findings "interesting." 

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Glatt, who is also a spokesperson for the Infectious Diseases Society of America, emphasized that the findings only show an association and not causation, and that much more clinical research is needed.

"Chlamydia pneumoniae is a very common respiratory pathogen that many people are exposed to throughout their lives," he told Fox News Digital. "While the study identifies a link between this bacterium and neurodegeneration, a standard sinus infection does not mean a patient will develop Alzheimer’s."

The key takeaway, according to Glatt, is that the study opens new doors for potential diagnostics and treatments, but is "not a reason for immediate alarm regarding common infections."

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Dr. Sharon Fekrat, MD, a clinical spokesperson for the American Academy of Ophthalmology and a retina specialist at the Duke University School of Medicine in North Carolina, agreed that the findings could help researchers better understand how inflammation may drive disease progression and "could lead to new ways to detect or treat Alzheimer’s in the future."

"This is early research suggesting that infection-related inflammation may worsen Alzheimer’s disease in people who are already vulnerable," Fekrat, who also did not work on the study, told Fox News Digital. "It does not mean infections cause Alzheimer’s or that people should worry about past respiratory illnesses."

While some teams are developing and testing retinal imaging tools in living patients, those methods are not yet part of routine clinical screenings or diagnosis, Fekrat noted.

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For now, the best proven steps include following brain-healthy habits, such as managing cardiovascular risk factors, staying mentally and socially engaged, and seeking medical care for any cognitive symptoms, the expert added.