Competitive co-infection model was used in which E058 or U17 and isogenic mutants were inoculated simultaneously. At 24 h post-infection, tissues were sampled, and results are presented as the log10 competitive index (CI). The CI represents the relative numbers of the two test strains from the tissues sampled (the output ratio) compared to the initial numbers of the strains in the inoculum (input ratio). Negative CI values indicate a decreased capacity for the mutant to compete with the virulent wild-type strain. Horizontal bars indicate the mean log10 CI values. Organs sampled were the heart (a), liver (b), spleen (c), lung (d), and kidney (e). Statistically significant decreases in CI values are indicated with asterisks (*, p<0.05; **, p<0.01).