FIG. 6.

Infection experiments probing the competitive indexes of PNPase-proficient MC1 and PNPase-deficient MC71 strains in BALB/c mice. Mice were challenged intraperitoneally with either a mixture of MC71 and MC1 (Tet^r) or MC71 spvR mutant and MC1spvR mutant (Tet^r). The bacteria were given at a ratio of 1:1 and in a total dose of approximately 5 × 10³ bacteria per mouse. Three days after infection, the mice were sacrificed for enumeration of the bacteria in the livers and spleens. The figure shows the ratios between MC1 (Tet^r) and MC71 (black columns), or MC1 spvR mutant (Tet^r) MC71spvR mutant (gray columns) and total bacterial loads. The competitions were carried out twice using five mice per competition each time, and the results are shown after the data from the two separate series of infections were combined. Asterisks show the level of significance (***, P < 0.001; Mann-Witney double-sided U test) when the ratios between the viable counts from competitions between MC71 and MC1 versus the MC71 spvR mutant to the MC1 spvR mutant in either the spleen or liver were compared.