Survival of RASV strains during low pH gastric transit. Histamine-treated mice were inoculated orally with 109 CFU of (A) χ9633(pYA4088, pWSK129), (B) χ9639(pYA4088, pWSK129), (C) χ9640(pYA4088, pWSK129) or (D) χ9558(pYA4088, pWSK129). Mice received either 1.3% sodium bicarbonate, chocolate Ensure® or no treatment prior to and immediately following immunization to neutralize gastric acid. The number of viable vaccine cells in the small intestine was quantified one hour after immunization. Data are presented as the number of CFU/g intestine of individual mice, with the geometric mean of the group displayed as a solid horizontal line. Groups that exhibited a significant increase (p < 0.05) in the number of viable vaccine cells in the small intestine over the control group are marked with an asterisk (*). Groups exhibiting a significant difference (p < 0.05) between Bicarbonate and Ensure treatments are marked with a double asterisk (**). Data are the combined results of two independent experiments (8 mice total).