Inclusion Criteria:

- Rheumatoid Arthritis (RA) patients must meet American College of Rheumatology (ACR)
criteria for RA

- RA patients: duration of disease will be greater than 6 weeks and less than 2 years.

- RA patients should have a Disease Activity Score 28 (DAS28) greater than or equal to
5.

- PsA patients will be required to have disease duration and DAS28 similar to the RA
patients, and to meet Moll and Wright criteria for PsA.

- Allowable medications for both groups at study entry will include: prednisone (or
equivalent) 5 mg or less per day (stable dose for at least 2 months); methotrexate 15
mg or less per week (stable dose for at least 2 months); and nonsteroidal
anti-inflammatory drugs (NSAIDs) at FDA-approved doses.

- Healthy controls will be age- and sex-matched individuals with no personal or family
history of inflammatory arthritis.

Exclusion Criteria:

- Patients who are unable to provide informed consent.

- Pregnant or lactating women.

- Recent (<3 months prior) use of any antibiotic therapy

- Current consumption of probiotics

- Current extreme diet (parenteral nutrition, macrobiotic diet, etc.)

- Prednisone >5 mg/day or equivalent

- Use of other disease-modifying antirheumatic drugs (DMARDs) with known antibiotic
properties (Gold salts, hydroxychloroquine, sulfasalazine or minocycline).

- Use of biologic DMARDs

- Known inflammatory bowel disease

- Known gastrointestinal (GI) tract neoplasm.

- Recent GI tract infection (gastroenteritis, colitis, diverticulitis, appendicitis)

- Chronic unexplained diarrhea.

- Any GI tract surgery leaving permanent residua (e.g., gastrectomy; bariatric surgery;
colectomy)

- Significant liver, renal or peptic ulcer disease, defined as:

- Liver: aspartate aminotransferase (AST)/alanine aminotransferase (ALT) > 2 x
upper limit of normal (ULN)

- Renal: Creatinine >1.5 or endstage renal disease

- Peptic ulcer disease: recent ulcer or GI bleed (within past 12 months)

- Inability or unwillingness to abstain from alcohol consumption.