The purpose of this study is to evaluate the safety and feasibility of kefir administration in critically ill adults.

Inclusion Criteria:

• Critically ill adult patients receiving antibiotics.
• Functional GI tract (able to tolerate oral diet or tube feeding).

Exclusion Criteria:

• Received antibiotics for >72 hours prior to enrollment.
• Known immunosuppression (due to medications including chronic steroids, TNF-alpha inhibitors, monoclonal antibodies, immunosuppressive antimetabolites, etc.).
• Compromised gut integrity (bowel resection, GI malignancy, GI bleed, inflammatory bowel disease).
• History of CDI within 60 days.
• Liver failure or pancreatitis.
• Dairy intolerance or milk allergy.
• Patients consuming probiotics at baseline.
• Artificial heart valve.
• Extremely poor prognosis and not expected to survive the treatment period.