Infection of Fungi and Bacteria in Brain Tissue From Elderly Persons and Patients With Alzheimer’s Disease | Frontiers in Aging Neuroscience

Alzheimer’s disease (AD) is the leading cause of dementia in elderly
people. The etiology of this disease remains a matter of intensive
research in many laboratories. We have advanced the idea that
disseminated fungal infection contributes to the etiology of AD. Thus,
we have demonstrated that fungal proteins and DNA are present in nervous
tissue from AD patients. More recently, we have reported that bacterial
infections can accompany these mycoses, suggesting that polymicrobial
infections exist in AD brains. In the present study, we have examined
fungal and bacterial infection in brain tissue from AD patients and
control subjects by immunohistochemistry. In addition, we have
documented the fungal and bacterial species in brain regions from AD
patients and control subjects by next-generation sequencing (NGS). Our
results from the analysis of ten AD patients reveal a variety of fungal
and bacterial species, although some were more prominent than others.
The fungal genera more prevalent in AD patients were Alternaria, Botrytis, Candida, and Malassezia.
We also compared these genera with those found in elderly and younger
subjects. One of the most prominent genera in control subjects was Fusarium.
Principal component analysis clearly indicated that fungi from frontal
cortex samples of AD brains clustered together and differed from those
of equivalent control subjects. Regarding bacterial infection, the
phylum Proteobacteria was the most prominent in both AD patients and controls, followed by Firmicutes, Actinobacteria, and Bacteroides. At the family level, Burkholderiaceae and Staphylococcaceae
exhibited higher percentages in AD brains than in control brains. These
findings could be of interest to guide targeted antimicrobial therapy
for AD patients. Moreover, the variety of microbial species in each
patient may constitute a basis for a better understanding of the
evolution and severity of clinical symptoms in each patient.

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