From the paper: "DSV [=Desulfovibrio bacteria] strains isolated from PD patients and healthy individuals appear to have different traits, but it is not yet known how to differentiate between them except as presented in this study."
It seems like everyone carries these bacteria but there are more harmful strains than others (but all of them seem to faciliate the aggregation of alpha-synuclein).
If everyone has the bacteria, it’s possible as well that it’s an idiosyncratic immune thing. Much like how everyone has the same flora on their skin, yet some people’s immune system overreacts and they get Seborrheic dermatitis; most others don’t.
