FIG 2.

IbaG augments V. cholerae resistance to cell envelope stressors and promotes intestinal colonization. (A) Growth curves of WT and ΔibaG V. cholerae grown in M9 medium. The OD₆₀₀ was measured at 10-min intervals. Experiments were done in biological triplicate; error bars show standard deviations. (B) Acid resistance was determined by calculating the proportion of cells that survived during growth in acidic medium (LB at pH 5.5) versus in LB at pH 7. The numbers of colony-forming units per milliliter (CFU/ml) were determined for WT and ΔibaG strains after 1-h growth in acidic medium from exponential-phase cultures. Experiments were performed in quadruplicate. (C) The MICs for the indicated agents were measured after 24 h growth in M9 medium at 37°C without shaking. The values shown represent the mean value obtained with two biological replicates done in technical quadruplicates for each strain. The concentrations are in micrograms per milliliter, except for bile, SDS, and deoxycholate which are shown as percentages. (D) Competitive indices for intestinal colonization for the indicated strain pairs. Suckling mice were inoculated with 1:1 mixture of ΔibaG mutant and a lacZ-negative derivative of WT, made from log-phase (OD₆₀₀ of ∼0.2) or overnight cultures. Competitive indices represent the output ratio (mutant strain CFU/lacZ mutant strain CFU) divided by the input ratio. Black horizontal lines represent geometric means, and colored horizontal lines show standard deviations. A Mann-Whitney U nonparametric test was used to assess statistical significance. Values that are significantly different are indicated by a bar and asterisks as follows: ***, P value of ≤0.0001; *, P value = 0.014.