Safety of Lactobacillus Reuteri in Healthy Children Ages 2 to 5 Years in Peru

Inclusion Criteria: * Children ages 2-5 years with no exclusion criteria Exclusion Criteria: * 1\) No enrollment of family members in households where any of the following are present: 1. Another study participant in the household 2. Pregnancy or current breastfeeding by any household member 3. Presence of an infant under age 6 months living in the household 4. Presence of immune suppressed individuals or use of immunosuppressive agents (including but not limited to corticosteroids and methotrexate, etc.) by any household member 5. Presence of a serious congenital anomaly or chronic medical condition that in the opinion of the investigators would contraindicate participation in any household member, including history of gastrointestinal surgery, chronic gastrointestinal illness, abnormal intestinal anatomy, or abnormal bowel functionality 2\) Allergy to penicillin or cephalosporins or gentamicin 3) History of antibiotic use in the last 30 days 4) Use of probiotic products within the past 90 days, including masato (local product with fermenting bacteria) and yogurt products containing live bacterial cultures. 5\) History of diarrheal illness within the past 30 days 6) Presence of fever or a pre-existing adverse event monitored in the study 7) Positive results on serum diagnostic tests for antibodies to HIV. Testing for Hepatitis B core antigen, and Hepatitis C is not necessary in children as in adults, since there is universal vaccination for Hepatitis B among children in this community, and both forms of hepatitis are rare and largely asymptomatic in this age group. 8\) Presence of severe anemia, defined as serum hemoglobin \< 8 gm/dL 9\) Out of range laboratory values for tests monitored as potential adverse events, as described in Appendix 2, B. LABORATORY VALUES, and detected based on Day 0 blood test results. However, subjects will only be excluded based on serum hemoglobin if they meet exclusion criterion 8. 10\) Pre-enrollment stool sample (collected within 14 days of Day 1 of the study) is positive for L. reuteri by PCR.