As of today (18-1-11), the 2013 reference has been cited by 15 others in Pubmed central. Some look relevant.
The role of small intestinal bacterial overgrowth in Parkinson's disease.
Mov Disord 2013 Aug;28(9):1241-9.
15 others:
ncbi.nlm.nih.gov/pubmed/?te....
Cited by 15 in PMC.