This pilot study is designed to determine if ingestion of Bacillus probiotics can cause alteration in levels of S. aureus colonization in the nose and intestine in preoperative orthopedic patients undergoing elective primary TJA.

Inclusion Criteria:

1. Adults (age >18 years)
2. Undergoing elective primary knee or hip arthroplasty
3. Confirmed colonization of nares and/or rectum with S. aureus or MRSA on routine standard-of-care preadmission testing
4. Written informed consent

Exclusion Criteria:

1. Regular use of a probiotic or prebiotic supplement within 3 months prior to enrollment
2. Antibiotic use within 3 months prior to enrollment
3. Active clinical infection
4. Participation in other clinical trials
5. Presence of pregnancy or lactation