Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 18.0-50.0,  Healthy Volunteer Male or female between 18 and 50 years of age, inclusive. 2. General good health, without clinically significant medical history, physical examination findings or clinical laboratory abnormalities per clinical judgment of the PI. 3. Completion of a training session and demonstration of comprehension of the protocol procedures and knowledge of ETEC-associated illness by passing a written examination. 4. Willingness to participate after informed consent obtained. 5. Availability for the study duration, including all planned follow-up visits. 6. Negative pregnancy test with understanding to not become pregnant during the study or within three months following last scheduled study visit  Presence of a significant medical condition which in the opinion of the investigator precludes participation in the study. 2. Significant abnormalities in screening hematology or serum chemistry as determined by PI or PI in consultation with the research monitor and sponsor. 3. Evidence of confirmed infection with HIV, Hepatitis B, or Hepatitis C. 4. Evidence of Immunoglobulin A (IgA) deficiency (serum IgA < 7 mg/dL or below the limit of detection of assay). 5. Evidence of current excessive alcohol consumption or drug dependence (a targeted drug screen may be used to evaluate at the clinician's discretion). 6. Evidence of impaired immune function. 7. Recent vaccination or receipt of an investigational product (within 30 days before receipt of challenge). 8. Any other which, in the investigator's opinion, would compromise the ability of the subject to participate in the study, the safety of the study, or the results of the study. 9. History of microbiologically confirmed ETEC or cholera infection in last 3 years. 10. Occupation involving handling of ETEC or Vibrio cholerae currently, or in the past 3 years. 11. Symptoms consistent with Travelers' Diarrhea concurrent with travel or planned travel to countries where ETEC infection is endemic. 12. Vaccination for or ingestion of ETEC, cholera, or E coli heat labile toxin within 3 years prior to dosing. 13. Any prior experimental infection with ETEC strain B7A. 14. Abnormal stool pattern. 15. Regular use of laxatives, antacids, or other agents to lower stomach acidity. 16. Use of any medication known to affect the immune function. 17. Known allergy to two of the following antibiotics: ciprofloxacin, trimethoprim-sulfamethoxazole, and amoxicillin