Table 6.
Region 3—Italy.
| Author/Country/Year * | Sample Number | Methodology | Microbiota Alteration in PD | Mechanisms (Theories) | Association | Limitations |
|---|---|---|---|---|---|---|
| Pietrucci et al., 2019, Italy [21]. | Cases: (n = 80) Controls: (n = 72) |
Fecal samples: 16S rRNA amplicon (V3–V4 regions) sequencing analysis PD-COMTi takers: 8. | - Higher levels in the feces compared to controls: Phylum: Proteobacteria, Firmicutes Family: Enterobacteriaceae, Lactobacillaceae, Enterococcaceae - Lower levels in the feces compared to controls: Phylum: Firmicutes Family: Lachnospiraceae - More abundant in PD- COMTi: Genus: Citrobacter, Enterococcus, Lactococcus, Klebsiella, Salmonella, Shigella, and an unclassified Enterobacteriaceae - Less abundant in PD- COMTi: Genus: Roseburia. |
Gut microorganisms metabolize phenylalanine, tryptophan, and tyrosine. This study found they were reduced in PD patients. An increase in the presence of Gram-negative bacteria leads to the elevation of LPS content. Thus, increasing intestinal permeability. | Yes | - Unbalanced cases and controls. - Age and sex. - Loss of 5 kg in the last year. |
| Cereda et al., 2018, Italy [22]. | Cases: (n = 193) Controls: (n = 113) | Fecal samples: 16S gene ribosomal RNA sequencing. | - Higher levels in fecal samples of PD compared to controls: Phylum: Verrucomicrobiota, Proteobacteria Family: Enterobacteriaceae, Lactobacillaceae, Coriobacteriaceae, Bifidobacteriaceae Genus: Akkermansia, Christensenellaceae, ParaBacteroides, Oscillospira - Lower levels in fecal samples of PD compared to controls: Family: Lachnospiraceae Genus: Roseburia, Ruminococcus. |
Production of SCFA such as butyrate, propionate, and acetate. Additionally, Lactobacillaceae is involved in the activity of the enteric nervous system and its secretion of α-synuclein and brain chemistry through the vagal nerve. | Yes | - Lack of sigmoid mucosal biopsies. - Lack of characterization of microbial functions through metagenomic analyses. - Presence of irritable bowel syndrome. |
* Case–control studies; cases were PD patients. PD: Parkinson’s disease; COMTi: catechol-O-methyltransferase inhibitors; LPS: lipopolysaccharides.