The purpose of this trial is to examine the safety and immunogenicity of Ty800 oral vaccine in healthy adult subjects.

Inclusion Criteria:

• Healthy Males or Females aged 18 to 55 years, inclusive
• Capable of understanding and complying with the protocol requirements and be available for the duration of the protocol

Exclusion Criteria:

• History of malignancy, immunocompromised conditions or currently receiving immunosuppressive treatment including systemic steroids
• History of Typhoid Fever infection, vaccination against typhoid fever or participation in a Clinical Trial using S.typhi organism at any time
• History of travel to a typhoid endemic region within the last 5 years or history of raising a child from an endemic area. Endemic regions are South and East Asia, the Indian Subcontinent, Africa and Central and South America including Mexico
• History of persistent diarrhea, blood in stool, peptic ulcer disease, or inflammatory bowel disease
• Allergies or sensitivities to antibiotics, notably quinolones, penicillins, sulfonamides, cefalosporins and chloramphenicol, and components of the buffer solution, notably aspartame.
• People who are commercial food handlers, day care workers, or health care workers involved in direct patient care. Also people with young children under 2 years of age at home or household contacts who are immunocompromised, pregnant or breast-feeding