Dose-Finding Study of CS19 Expressing ETEC Challenge Strains

Inclusion Criteria: 1. Male or female between 18 and 45 years of age, inclusive. 2. General good health, without significant medical illness, abnormal physical examination findings or clinical laboratory abnormalities as determined by principal investigator (PI) or PI in consultation with the medical monitor and Sponsor. 3. Demonstrate comprehension of the protocol procedures and knowledge of ETEC illness by passing a written examination (pass grade ≥ 70%) 4. Willing to participate after informed consent obtained. 5. Available for entire inpatient portion of study and all outpatient study visits. 6. Negative serum pregnancy test at screening (initial visit and day -7 to - 3) and a negative urine pregnancy test on the day of admission to the inpatient phase for female subjects of childbearing potential. Females of childbearing potential must agree to use an efficacious hormonal or barrier method of birth control during the study. Alternatively, abstinence alone is acceptable. Female subjects who are unable to bear children must provide supporting documentation (e.g., prior tubal ligation or hysterectomy). Exclusion Criteria: 1. Presence of a significant medical condition, (e.g., psychiatric conditions or gastrointestinal disease, such as peptic ulcer, symptoms or evidence of active gastritis or gastroesophageal reflux disease, inflammatory bowel disease, alcohol or illicit drug abuse/dependency), or other laboratory abnormalities which in the opinion of the investigator precludes participation in the study. 2. Immunosuppressive illness or IgA deficiency (below the normal limits) 3. Positive serology results for HIV, HBsAg, or HCV antibodies. 4. Significant abnormalities in screening laboratory hematology, serum chemistry, urinalysis, as determined by PI or PI in consultation with the medical monitor and Sponsor. 5. Allergy to fluoroquinolones, cotrimoxazole, or ampicillin/penicillin (excluded if allergic to two of three). 6. Fewer than 3 stools per week or more than 3 stools per day as the usual frequency; loose or liquid stools other than on an occasional basis. 7. History of diarrhea in the 2 weeks prior to planned inpatient phase. 8. Regular use of laxatives or any agent that increases gastric pH (regular defined as at least weekly). 9. Use of antibiotics during the 7 days before bacterial dosing or proton pump inhibitors, H2 blockers, or antacids within 48 hours of dosing. 10. Travel to countries where ETEC or cholera infection is endemic (most of the developing world) within two years prior to dosing. 11. History of vaccination for or ingestion of ETEC, cholera, or LT toxin. 12. Stool culture (collected no more than 1 week prior to admission) positive for ETEC or other bacterial enteric pathogens (Salmonella, Shigella and Campylobacter). 13. Use of any investigational product within 30 days preceding the receipt of the challenge inoculum, or planned use during the active study period. 14. Use of any medication known to affect the immune function (e.g., corticosteroids) within 30 days preceding receipt of the challenge inoculum or planned use during the active study period. (Topical and intra-articular steroids will not exclude subjects). MANAGEMENT