CVD 37000: Immunity and Microbiome Studies at Intestinal and Systemic Sites in Ty21a Vaccinated Adults

Inclusion Criteria: * Age 18 years and older * Undergoing colonoscopy for screening or surveillance for colorectal cancer at the University of Maryland * Provide written informed consent prior to initiation of any study procedures * Healthy, as defined by considered fit to undergo outpatient elective colonoscopy by the referring health care provider Exclusion Criteria: * Pregnancy or nursing mother * Known coagulopathy or bleeding disorder preventing mucosal biopsy * History of Crohn's disease or ulcerative colitis * Surgical removal of the ileocecal valve or any part of the small or large intestine * Allergic reaction to oral typhoid vaccine in the past * Immunosuppression from illness or treatment, including * immune-deficiency disorders such as Human Immunodeficiency Virus (HIV) or Acquired Immunodeficiency Syndrome (AIDS) * leukemia, lymphoma, or cancers * immune suppressive medications or treatments, such as corticosteroids or radiation * Receipt of any other vaccine two weeks prior to receipt of Ty21a * Positive urine pregnancy test (HCG) prior to colonoscopy or vaccination