Bottleneck during acquisition of <i>B. burgdorferi</i> by fed larval ticks.

<p>Mixed BbITS infections were initiated by injecting mice with a combined inoculum of 3.5×10⁴ organisms, with each of 7 tagged clones (A to G) present at an infectious dose of 5×10³ spirochetes. Cohorts of larval ticks were fed on 9 infected mice at 8 weeks of infection and spirochetes isolated from ∼10 individual replete ticks per mouse. Genomic DNA of <i>B. burgdorferi</i> isolates was used in PCR screens to identify the BbITS present in both mice and ticks. An example of these data from a single infected mouse/fed tick cohort is shown in (<b>A</b>). Each tagged clone, identified at the head of each column, is represented by a different color, and the presence of a color block denotes detection of this clone in ear tissue at the indicated time (upper section), or acquired by individual replete ticks (lower section). These data pertain to mouse/tick set #1 of (<b>B</b>), in which the data for all 9 mouse/tick cohorts are summarized. Bars, identified in the key at the top of the graph, indicate the number of BbITS collectively present in each larval tick cohort, the average number of BbITS per individual tick in each cohort, and the total number of BbITS in the ear punch biopsy of each mouse on which these ticks fed. Error bars show standard deviation from the mean. A Mann-Whitney non-parametric test was used to compare the collective data for the total number of BbITS acquired by a larval tick cohort versus the number of BbITS present in an individual tick within the same larval cohort (P = 0.002).