Bacteria in the gut may be a cause of Parkinson’s disease, study finds

“The findings indicate that specific strains of Desulfovibrio bacteria are likely to cause Parkinson’s disease. The disease is primarily caused by environmental factors, that is, environmental exposure to the Desulfovibrio bacterial strains that cause Parkinson’s disease,” said Professor Per Saris from the University of Helsinki in an official release.

Certain strains of this bacteria excrete compounds that cause neuronal proteins, alpha-synuclein, found inside brain cells to form toxic clumps. These proteins are generally studied to examine the pathology of this debilitating disease.

The researchers tried to investigate if the Desulfovibrio strains found in Parkinson's patients caused the formation of these protein clumps or not. The team conducted this study on the model organism: the worm Caenorhabditis elegans. These worms were fed with Desulfovibrio bacteria obtained from Parkinson's patients.

The findings show that the presence of these bacteria strains caused significant aggregation of the α-synuclein protein in a model organism for Parkinson's disease. 

However, the results showed that Desulfovibrio strains isolated from healthy individuals did not cause the same level of protein accumulation. While the clumps formed by these bacteria strains in Parkinson's disease patients were also found to be larger.

“Our findings make it possible to screen for the carriers of these harmful Desulfovibrio bacteria. Consequently, they can be targeted by measures to remove these strains from the gut, potentially alleviating and slowing the symptoms of patients with Parkinson’s disease. Once the Desulfovibrio bacteria are eliminated from the gut, α-synuclein aggregates are no longer formed in intestinal cells, from which they travel towards the brain via the vagus nerve like prion proteins,” concludes Saris. 

The study is conducted by researchers from the University of Helsinki and the University of Eastern Finland. The study has been published in the journal Frontiers in Cellular and Infection Microbiology.

Study abstract:

Introduction: The aggregation of the neuronal protein alpha-synuclein (alpha-syn) is a key feature in the pathology of Parkinson’s disease (PD). Alpha-syn aggregation has been suggested to be induced in the gut cells by pathogenic gut microbes such as Desulfovibrio bacteria, which has been shown to be associated with PD. This study aimed to investigate whether Desulfovibrio bacteria induce alpha-syn aggregation.

Methods: Fecal samples of ten PD patients and their healthy spouses were collected for molecular detection of Desulfovibrio species, followed by bacterial isolation. Isolated Desulfovibrio strains were used as diets to feed Caenorhabditis elegans nematodes which overexpress human alpha-syn fused with yellow fluorescence protein. Curli-producing Escherichia coli MC4100, which has been shown to facilitate alpha-syn aggregation in animal models, was used as a control bacterial strain, and E. coli LSR11, incapable of producing curli, was used as another control strain. The head sections of the worms were imaged using confocal microscopy. We also performed survival assay to determine the effect of Desulfovibrio bacteria on the survival of the nematodes.