Bacterial burdens in aged mice are reduced early in the infection.

Young and aged mice were intranasally infected and their lungs, spleen and blood were harvested, processed, and plated in order to determine the bacterial burden (n = 3–4 mice per group). Panel A shows a significant reduction in the number of bacteria recovered from the lungs of aged mice as compared to young mice throughout the course of infection, especially at 1 and 3 DPI. Panel B indicates a reduction in systemic dissemination in the blood between young mice and aged mice that could be considered potentially moribund and aged mice that seemed to be able to control the infection. Panel C shows the bacterial burden in the spleen and similarly indicates a reduction in the amount bacteria recovered from aged mice (survivors and non-survivors) relative to young mice. * p<.05; **p<.005; ***p<.001.