FIG 8 .

CsrA is required for V. cholerae virulence in infant mice. The CsrA Arg6His point mutant NcsrA.R6H was competed against the wild-type strain N16961G. Five-day-old suckling BALB/c mice were inoculated intragastrically with an equal number of each competing strain as described in Materials and Methods. The competitive index (CI) was calculated by normalizing the output ratio to the input ratio of the two competing strains. Each data point represents one mouse, and the median CI (0.01) is represented by the solid horizontal line. A CI value below 1 indicates that the mutant is at a competitive disadvantage. The dotted line shows the limit of detection for the CI in this experiment, which was 0.005. In 4 out of 9 mice, the mutant was not detected during analysis of more than 200 recovered colonies, and thus the CI falls below the limit of detection. These data points are included in the analysis as having a value of 0.005, which is the most conservative estimate for the CI. The actual CI values are likely to be lower. The results were statistically significant (P < 0.05) by the Mann-Whitney nonparametric test.