Inclusion Criteria:

• Age 18 - 40 years, inclusive.
• Good general health as determined by a screening evaluation within 30 days before administration of CVD 909 or placebo.
• Expressed interest and availability to fulfill the study requirements.
• Informed, written consent.
• Agrees not to participate in another investigational vaccine or drug trial for the first 84 days of this study.
• Agrees not to become pregnant from the time of study enrollment until at least 56 days after the administration of CVD 909 or placebo; if a woman is sexually active and capable of conception (i.e., no history of hysterectomy or tubal ligation), she must agree to use hormonal or barrier birth control. A woman is eligible if she is monogamous with a vasectomized male.

Exclusion Criteria:

• History of any of the following medical illnesses:
• Gall bladder disease or gall stones without cholecystectomy
• Diabetes
• Cancer
• Heart disease (hospitalization for a heart attack, arrhythmia, or syncope)
• Unconsciousness
• Seizures (other than febrile seizures as a child less than 5 years old)
• Recurrent infections (more than 3 hospitalizations for invasive bacterial infections such as pneumonia or meningitis)
• Any current illness requiring daily medication other than vitamins, birth control, or stable regimen of anti-histamine medication for hay fever or anti-depressant
• History of the following types of abdominal surgery:
• Any major gastrointestinal surgery (e.g., intestinal resection or splenectomy)
• A laparotomy for any reason (e.g., hysterectomy, Caesarean section, appendectomy, or herniorrhaphy) within the last 3 years
• Laparoscopic abdominal surgery within the past year
• A large abdominal scar of unclear origin
• Evidence of gastrointestinal disease, as indicated by any of the following:
• Usual bowel habit of more than 3 bowel movements each day
• Recurrent diarrhea (greater than 5 episodes during the past 6 months, each lasting at least 3 days, with at least one week between episodes)
• Lactose intolerance
• Frequent indigestion or heartburn that requires daily antacids or other medical therapy
• Diagnosed by a doctor as having irritable bowel disease, Crohn's disease, ulcerative colitis, celiac disease, stomach or intestinal ulcers in the past 10 years
• Blood in the stool during the past year (other than occasional small amount from straining)
• Any clinically significant abnormality detected on physical examination, including:
• Murmur (other than a functional murmur)
• Focal neurological deficit suggesting a pathologic process
• Hepatosplenomegaly
• Lymphadenopathy
• Jaundice
• Hypertension (BP greater than 150/90 mm Hg on two separate days) or hypotension (BP less than 85/55 mm Hg)
• Any lab abnormality, as listed below:
• WBC outside the normal range
• Hemoglobin outside the normal range
• Platelet count outside the normal range
• Creatinine outside the normal range
• Fasting glucose greater than 115 mg/dl (if screening greater than 115 mg/dl)
• AST or ALT outside the normal range (may be repeated once if outside this limit)
• Positive serology for hepatitis C or HIV antibody or hepatitis B surface antigen
• Stool culture positive for Salmonella spp, Shigella spp, Campylobacter jejuni, V. cholerae, or pathogenic protozoa
• For women, positive serum pregnancy test within 7 days and urine pregnancy test within 24 hours of administering CVD 909 and within 24 hours of administering Vi vaccine
• Nursing mother
• Oral temperature greater than 37.8ºC or symptoms of an acute self-limited illness such as an upper respiratory infection or gastroenteritis on the day of administration of CVD 909 or placebo
• Immunization against typhoid fever or history of typhoid fever
• Allergy to quinolones (including ciprofloxacin) or sulfa drugs (Including trimethoprim/sulfamethoxazole)
• Medical, occupational, or family problems as a result of alcohol or illicit drug use during the past 12 months
• Failure to pass written examination about study purpose, background, and procedures (70% correct answers required to pass)
• Receipt of an investigational vaccine or drug within 28 days before administration of CVD 909
• Commercial food-handlers
• Health care workers who are engaged in patient care during the study
• Day care providers
• Subject with a household contact who is less than 2 years of age, who is immunocompromised or pregnant, or who works as a commercial food-handler
• Use of antibiotics within 7 days of CVD 909 or placebo vaccination
• Other condition that in the opinion of the investigator would jeopardize the safety or rights of a volunteer participating in the trial or would render the subject unable to comply with the protocol.