FIG 6.

In vitro and in vivo competition between null and wild-type strains. The competitive index (CI) was calculated by normalizing the output ratio to the input ratio of the two competing strains. (A) Relative fitness of the wild-type and null strains was assessed in vitro in the presence of oxygen (atmospheric oxygen conditions) and absence of oxygen (anaerobic chamber). Each point represents an individual culture. The lines indicate the means and standard deviations. (B) Relative fitness of the wild-type and null strains was assessed in the infant mouse infection model. Each circle indicates a separate infant mouse, and horizontal lines indicate the means and standard deviations. A competitive index of <1 indicates a fitness defect for the null mutant under the condition.