Fig 5.

The S. aureus MW2 norD mutant exhibits a fitness defect in the murine subcutaneous abscesses. (A) Fitness competition between S. aureus MW2 and MW2 opp1, MW2 norD, and MW2^SM mutants in the murine subcutaneous abscess model. Exponential-phase bacteria, together with Cytodex beads, were injected subcutaneously in both flanks of each mouse at a typical input ratio for each bacterial strain of 1:1. The inoculum was 1 × 10⁶ to 5 × 10⁶ CFU in 0.2 ml for each lesion. After 48 h, the bacterial load of each abscess was estimated by quantitative plate cultures. For in vitro TSB cultures, the numbers of bacteria were determined after 24 h. Competitor strains were distinguished by resistance to streptomycin in strain MW2^SM. A competitive index (CI) was calculated as the output ratio of two strains divided by the input ratio. Each circle represents the CI for one abscess, and the horizontal bars represent medians for the group. (B and C) Growth curves of strains cultivated in TSB broth at 37°C. Representative results of repeated experiments are shown. (D) The fitness defect of the MW2 norD mutant in murine subcutaneous abscesses was complemented by plasmid-encoded NorD. All strains competed with MW2^SM(pOS1-Plgt) as described above. The data shown in panels A and D are the results compiled from three independent experiments. An asterisk indicates that the median CI is significantly different from one.