Dose-finding Study of WS6788A, DS37-4 and H10407 Enterotoxigenic Escherichia Coli (ETEC) Challenge Strains

Inclusion Criteria: Healthy adults age 18 to 45 years old who are willing to participate, complete training on ETEC and diarrhea and procedures of the protocol, pass the test documenting knowledge of the study, and give informed consent. Exclusion Criteria: age<18 or >45 years Chronic illness, chemical dependency, or significant medical illness as determined by the investigator. immunosuppressive condition or IgA (Immunoglobulin A) deficiency HIV antibody positive hepatitis B surface antigen positive hepatitis C antibody positive travel to ETEC endemic area within 2 years vaccination or other exposure to ETEC, cholera, or heat labile toxin (LT) toxin within 3 years pregnancy as defined by + serum or urine - human chorionic gonadotropin (HCG) on the day before immunization inability to pass the written examination use of antibiotic, H2 blocking agent or proton pump inhibitor within 7 days of challenge regular use of laxatives antacids or other agents to lower stomach acidity significant abnormality in screening lav hematology and chemistry tests as determined by the investigator. significant abnormality on EKG for those 40 to 50 years old as determined by the investigator. allergy to quinolones, penicillin's and Bactrim. abnormal stool pattern (fewer than 3 stools per week or more than 3 stools per day).