Amyloidogenic amyloid-β-peptide variants induce microbial agglutination and exert antimicrobial activity

Amyloid-β (Aβ) peptides are the main components of the plaques found in the brains of patients with Alzheimer’s disease. However, Aβ peptides are also detectable in secretory compartments and peripheral blood contains a complex mixture of more than 40 different modified and/or N- and C-terminally truncated Aβ peptides. Recently, anti-infective properties of Aβ peptides have been reported. Here, we investigated the interaction of Aβ peptides of different lengths with various bacterial strains and the yeast Candida albicans. The amyloidogenic peptides Aβ(1-42), Aβ(2-42), and Aβ(3p-42) but not the non-amyloidogenic peptides Aβ(1-40) and Aβ(2-40) bound to microbial surfaces. As observed by immunocytochemistry, scanning electron microscopy and Gram staining, treatment of several bacterial strains and Candida albicans with Aβ peptide variants ending at position 42 (Aβ(x-42)) caused the formation of large agglutinates. These aggregates were not detected after incubation with Aβ(x-40). Furthermore, Aβ(x-42) exerted an antimicrobial activity on all tested pathogens, killing up to 80% of microorganisms within 6 h. Aβ(1-40) only had a moderate antimicrobial activity against C. albicans. Agglutination of Aβ(1-42) was accelerated in the presence of microorganisms. These data demonstrate that the amyloidogenic Aβ(x-42) variants have antimicrobial activity and may therefore act as antimicrobial peptides in the immune system.