New York, Dec 3 (IANS): US scientists in a breakthrough research have discovered a functional link between bacteria in the intestines and Parkinson's disease.

Parkinson's disease -- a disorder of the central nervous system that affects movement, often including tremors -- affects up to 10 million people worldwide.

The study showed that changes in the composition of gut bacterial populations could affect motor skills.

"The gut is a permanent home to beneficial and sometimes harmful bacteria, microbiome, important for the development and function of the immune and nervous systems," said Sarkis Mazmanian, Professor at California Institute of Technology in the US.

The researchers hypothesised that gut bacteria may contribute to Parkinson's as 75 per cent with the disease have gastrointestinal abnormalities, primarily constipation which often precede the disease.

For the study, the team used two groups of mice genetically programmed to overproduce alpha-synuclein -- protein associated with damage in the brains of Parkinson's patients.

One group of mice had a complex consortium of gut bacteria, the others, called germ-free mice, were bred in a completely sterile environment and thus lacked gut bacteria.

The results showed that the germ-free mice performed significantly better than the mice with a complete microbiome.

All three hallmark traits of Parkinson's -- tremors and difficulty walking, aggregation of alpha-synuclein within brain cells and gut as well as the presence of cytokines were absent in germ-free mice, the researchers observed.

In addition, gut bacteria were also found to break down dietary fibre to produce molecules called short-chain fatty acids (SCFAs). An imbalance in these regulates brain inflammation and triggers other symptoms of Parkinson's, the study noted.

The findings, published in the journal Cell, may lead to safer therapies, such as drugs to kill gut bugs or probiotics with fewer side effects compared to current treatments.