A bottleneck limits dissemination of <i>Y. pestis</i> to the draining LN.

<p>(A and B) Southern dot blot analysis of DNA from bacteria from (A) LNs harvested at 12 hpi and (B) LNs and spleens at 48 hpi. Each row shows results from a single mouse (identified with a number). The number of CFU obtained from each tissue and from which DNA was extracted is also shown. Representative blots are shown for A and B. A dose of 211 CFU was used. Plates that were completely covered with a layer of bacteria (as opposed to isolated colonies) are identified as “lawn”. (C) Number of tagged strains in LNs after ID (black) or SC (white) inoculation at 48 hpi. A dose of 303 CFU and 331 CFU were used for the ID and SC inoculations, respectively. Each symbol represents a value from an individual mouse. Bars indicate medians per group. Results from two combined experiments are shown. (D) Number of tagged strains in ears (triangles) and LNs [circles at 12 hpi (black) and 48 hpi (white)]. A dose of 226 CFU was used. (E) Bacterial burden from LNs 48 h after the first of two consecutive inoculations. Mice were inoculated first with carbenicillin resistant <i>Y. pestis</i> (652 CFU) and, 24 h later, with kanamycin resistant <i>Y. pestis</i> (<i>Yp/Yp</i>, 449 CFU). Another group of mice was mock inoculated with PBS and, 24 h later, inoculated with kanamycin resistant <i>Y. pestis</i> (PBS/<i>Yp</i>, 449 CFU). The dotted line represents the limit of detection. Each symbol represents a value from an individual mouse. Bars indicate medians per group. The Wilcoxon matched-pairs signed-rank test (D) or the Mann Whitney test (C) and (E) was used to determine statistical significance and the p value is shown. Differences between groups were considered to be statistically significant when p < 0.05. Experiments were performed a minimum of 3 times and data from representative experiments are shown.