Prevalence of proinflammatory gut bacteria increases in faecal samples from patients suffering from Alzheimer's dementia

Alzheimer's disease (AD) is the most common form of global dementia, characterised by an irreversible decline in cognitive function. The pathogenesis of several neurodegenerative disorders has been linked to dysbiosis of the gut microbiota via bidirectional communication though the gut-brain axis. We set out to establish whether there were any differences in the composition or function of the gut microbiota between elderly people with or without AD diagnosis, resident in care home environments. Based on the results of 16S rRNA gene profiling we established that AD sufferers had increased levels of Escherichia/Shigella and Clostridium_sensu_stricto_1, and decreased levels of Bacteroides, Blautia and Roseburia species. The increased levels of potentially pro-inflammatory bacteria was consistent with slightly higher concentrations of calprotectin, a biomarker of gut inflammation. Levels of most microbial metabolites measured were similar across groups, although AD sufferers had significantly increased proportions of the branched chain fatty acid, iso-butyrate and a decreased proportion of the short-chain fatty acid butyrate. Taken together these results show that Alzheimer's sufferers have several key differences within their gut microbiota profile. The dysbiotic microbiome included both compositional and functional changes linked to poorer health and gut inflammation.