Study to Assess the Safety of MRx0029 or MRx0005 Compared to Placebo, in People With Parkinson's

Inclusion Criteria: Diagnosis of idiopathic PD according to the UKPDS-BBCDC Able to understand and willing to provide informed consent and able to comply with the study procedures and restrictions. Male or female participants age ≥ 40 or ≤ 85 years of age. BMI ≥ 18.0 to ≤ 35.0 kg/m2, inclusive, where BMI (kg/m2) is calculated by body weight (kg)/height2 (m2). Hoehn & Yahr (H&Y) Stage I to II (if on levodopa the participant should be classed as Stage I to II in an 'ON' period) A documented diagnosis of PD If presently being medically treated for PD, they should be on a stable dose unchanged within the 30 days prior to screening and not be expected to require any adjustments or start any new PD medication for the duration of their participation in the study. No clinically relevant abnormal medical history, or abnormal findings on physical examination, vital signs, ECG, or laboratory tests Has been fully vaccinated with an approved Covid-19 vaccine Male and female participants are eligible to enter provided they follow the contraception criteria for the study. Exclusion Criteria: Participants with significant motor fluctuations Parkinson syndromes Known carriers of familial PD genes History and/or current presence of clinically significant CNS disease other than PD. Montreal Cognitive Assessment (MoCA) <24 No history of spontaneous constipation since diagnosis Participants who are <70% compliant to completing their e-daily assessed at Treatment Period 1, Day 1. Are non-compliant with prescribed PD medication Comorbidities that have not been optimally controlled for the last 3 months prior to screening. Participants with known Type 1 or Type 2 diabetes mellitus or a HbAlc result. indicative of diabetes/pre-diabetes. Have an active or recent malignant disease or any concomitant end-stage organ disease. Participants with known GI fistula, feeding tubes, or inflammatory bowel disease. Participants who had recent abdominal surgery (6 months before the screening visit). Participants with GI disease resulting in an inability to take oral medication, malabsorption syndrome, prior surgical procedures affecting absorption, uncontrolled GI disease Participants with conditions that may increase the risk of generalized peritonitis Dysphagia to the extent it would affect the participant's ability to swallow the IMP during their participation Anything which in the opinion of the investigator prevents the participant being able to give urine or stool samples. Positive serology for hepatitis B surface antigen (HBsAg), hepatitis C virus antibody (anti-HCV), or human immunodeficiency virus antibodies (anti HIV) 1/2 at screening. Previous history or current active tuberculosis (TB), or taking medication for the treatment of TB. Participant has severe or moderate renal impairment (defined as creatinine clearance <60 mL/min) estimated using Cockcroft-Gault Equation. Participants taking anti-cholinergic medication or amantadine. Participants with congenital, acquired or drug-related immunodeficiency. Participants who use systemic corticosteroids or systemic immunosuppressants for any reason within 30 days prior to screening. Participants taking ad hoc anti-inflammatory medication within 30 days of screening are excluded. Participants taking dopamine antagonists, such as the neuroleptics or metoclopramide are excluded. Participants who are allergic to the following antibiotics: amoxicillin/clavulanic acid, ampicillin, chloramphenicol, clarithromycin, clindamycin, imipenem, or metronidazole. Participants who have completed a course of systemic antibiotics in the 30 days prior to screening. Participants using prebiotic and probiotic supplements Donation or loss of 500 mL blood during the 3 months before screening. Current or history of alcohol or drug abuse or other dependence (except nicotine dependence) within the last 2 years prior to IMP administration. Positive urine drug screen (if not due to concomitant medication) or alcohol breath test. Receipt of a positive COVID-19 test result Participant is currently enrolled in or has not yet completed at least 30 days since ending other investigational device or study drug(s), or participant receiving other investigational agent(s). Received a live vaccine within 4 weeks prior to enrolling in this trial or plan for any such vaccination during the trial or within 4 months after study drug administration. Administration of inactivated vaccines (for example, inactivated influenza vaccines is allowed.). Legal incapacity or limited legal capacity.