Colocalization of the β amyloid peptide with bacteria in postmortem brain tissue of patients with familial Alzheimer's disease

Background β‐amyloid (βA) is a highly conserved peptide throughout the evolution of species that has been proposed as a participant in vital functions. This peptide has been related to the onset and progression of Alzheimer’s disease (AD). Additionally, recent scientific reports have demonstrated in vitro activity against bacteria, fungi and virus. The aim of this study is to describe the colocalization between βA and bacteria in postmortem brain tissue of patients with familial AD. Method Initially, we observed bacterial accumulations in brain tissue of two patients with familial Alzheimer's disease and in one case colocalization of βA with bacteria was observed. In order to confirm whether this finding was repeated, shortly after donation and before being fixed with formaldehyde, five cases fresh cerebral samples from five cases with early onset AD were immediately inoculated in vitro with Enterococcus faecalis and Lactobacillus rhamnosus. After different periods of time, both immunostaining for βA detection and Gram staining for bacteria observation were performed on each sample. Result Colocalization of βA and gram positive bacteria were observed in all cases. In those infected in vitro, the phenomenon was observed after a period of 24 h of incubation at 35 °C. In the cases fixed with formaldehyde to 10%, its observed multiples cavitations macroscopic in white substance throughout the brain Conclusion These results suggest that the βA agglutinates the bacteria, then it’s possible a relationship between βA and bacteria, possibly due to the antimicrobial activity that has been attributed to βA. However, it is necessary to carry out studies with a larger number of samples to confirm the phenomenon and to attempt to explicate it from the cellular and molecular points of view.