Figure 4. Survival of strains cultured under acid resistance-inducing conditions.

Wild-type enteric strains were grown to stationary phase in TSB medium containing 0.4% glucose under anaerobic conditions. (A) Cells were challenged in EG medium (pH 3.0) containing 0.1% casamino acids. Survival was assayed hourly for 4 h by plating onto LB agar. Data shown are the mean and SEM of three independent experiments. (B) Mice were either fasted for 6 h (fasted mouse model) or fasted and low gastric pH was induced by histamine injection (histamine mouse model) and then inoculated with 10⁹ CFU of each strain. Sixty min after inoculation, mice were euthanized and the entire small intestine removed and homogenized. Strain survival was assayed by plating onto LB agar containing kanamycin. Data are expressed as the percent of initial inoculum recovered (% survival). The geometric mean and 95% confidence interval of two independent experiments (8 mice total) is depicted.