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Editors have highlighted the following attributes while ensuring the content's credibility: fact-checked peer-reviewed publication trusted source proofread The GIST Add as preferred source --------------------------------------------------------------------- Common bacteria discovered in the eye linked to cognitive decline Chlamydia pneumonia detected in the human retina by specific monoclonal antibody (red), and DNA probe (green) and nuclei (blue). Credit: Image courtesy of Maya Koronyo-Hamaoui Chlamydia pneumoniae--a common bacterium that causes pneumonia and sinus infections--can linger in the eye and brain for years and may aggravate Alzheimer's disease, according to a study from Cedars-Sinai. Published in Nature Communications, the discovery suggests this bacterium can amplify Alzheimer's disease and points to potential interventions including inflammation-limiting therapies and early antibiotic treatment. Bacteria reach the eye and brain The study shows for the first time that Chlamydia pneumoniae can reach the retina--the tissue lining the back of the eye--where it triggers immune responses linked to inflammation, nerve cell death and cognitive decline. "Seeing Chlamydia pneumoniae consistently across human tissues, cell cultures and animal models allowed us to identify a previously unrecognized link between bacterial infection, inflammation and neurodegeneration," said Maya Koronyo-Hamaoui, Ph.D., professor of Neurosurgery, Neurology, and Biomedical Sciences at Cedars-Sinai Health Sciences University and the leading, senior author of the study. "The eye is a surrogate for the brain, and this study shows that retinal bacterial infection and chronic inflammation can reflect brain pathology and predict disease status, supporting retinal imaging as a noninvasive way to identify people at risk for Alzheimer's." How the study was conducted To conduct the study, researchers used advanced imaging, genetic testing and protein analysis to examine retinal tissue from 104 individuals, some with normal cognition, some with mild cognitive impairment and some with Alzheimer's disease. They found significantly higher levels of Chlamydia pneumoniae in the retinas and brains of people with Alzheimer's disease than they found in people with normal cognition. The higher the bacterial levels detected, the more severe the brain changes and cognitive decline investigators found. Higher levels of the bacterium were more common in people who carried the APOE4 gene variant, a known risk factor for Alzheimer's disease. Links to inflammation and treatment ideas Investigators also studied human neurons in the lab and in laboratory mice with Alzheimer's disease. In both, infection with Chlamydia pneumoniae increased inflammation, nerve cell death and cognitive decline, showing the bacterium can accelerate disease processes. The infection also triggered production of amyloid-beta, the protein that accumulates in the brains of people with Alzheimer's. The findings were driven by co-first authors Bhakta Gaire, Ph.D., and Yosef Koronyo, MSc. "This discovery raises the possibility of targeting the infection-inflammation axis to treat Alzheimer's," said Timothy Crother, Ph.D., co-corresponding author of the study and research professor at Cedars-Sinai Guerin Children's and the Department of Biomedical Sciences at Cedars-Sinai. The findings suggest that targeting chronic bacterial infection--and the inflammation it triggers--could represent a new treatment strategy. The research also supports potential use of the retina as a noninvasive way to help diagnose and monitor the disease. Publication details Bhakta Prasad Gaire et al, Identification of Chlamydia pneumoniae and NLRP3 inflammasome activation in Alzheimer's disease retina, Nature Communications (2026). DOI: 10.1038/s41467-026-68580-4 Journal information: Nature Communications Key medical concepts Alzheimer's DiseaseRetinaAmyloid beta-PeptidesApolipoprotein E4 Clinical categories NeurologyOphthalmologyInfectious diseases Provided by Cedars-Sinai Medical Center Citation: Common bacteria discovered in the eye linked to cognitive decline (2026, February 2) retrieved 2 February 2026 from https:// medicalxpress.com/news/ 2026-02-common-bacteria-eye-linked-cognitive.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. --------------------------------------------------------------------- Explore further Proteins in eye's nerve cells linked to Alzheimer's disease --------------------------------------------------------------------- 33 shares * Facebook * Twitter * Email Feedback to editors * Trending * Featured * Last Comments Study maps 30 rheumatoid arthritis biopsies, linking joint scarring to treatment resistance Jan 31, 2026 0 Gut bacteria may tip the balance between feeding tumors and fueling immunity Jan 30, 2026 0 Exposing a 'mental trap': The hidden bias behind chronic indecision Jan 31, 2026 1 Rethinking longevity: Genes account for 50% of human lifespan variation, study suggests Feb 1, 2026 1 Night owl or early bird: Chronotype can influence your health and muscle strength Jan 30, 2026 0 --------------------------------------------------------------------- [gif] Chemo before 3 pm could be more successful for lung cancer patients 11 minutes ago [gif] Our body is doing fat-math (better than you'd imagine) 21 minutes ago [gif] 'Ghost' providers hinder access to health care for Medicaid patients 52 minutes ago [gif] A more reliable platform to test antibody medicines 1 hour ago [gif] Shingles vaccination associated with delayed dementia onset in older adults 1 hour ago [gif] Can metabolism tune heart aging? 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