Comparison of splenic weight between RB51 and B. abortus ΔpurD mutant mice groups. Splenic weight comparison of the RB51 and B. abortus ΔpurD mutant mice groups infected with 3 X108 CFU/ dose of the RB51 and B. abortus ΔpurD mutant at 10th and 20th DPI. Error bars represent average values ± the standard deviations. The asterisks denote values that are significantly different (*P <0.05) between groups with the parent RB51 and the B. abortus ΔpurD mutant at each time point, as determined by two away ANOVA.