FIG. 1.

B. burgdorferi N40 growth during coculture with tick cells: mean fold increases (± standard errors of the means) in B. burgdorferi N40 levels 4 days after inoculation into L15BS medium alone, into L15BS medium in the presence of tick cells (MOI, 10), and into BSK-H medium. The concentration of inoculated Borrelia cells was 2 × 10⁷ to 4 × 10⁷ cells/ml in each case. The results obtained with the ISE6 and IDE8 tick cell lines were similar and were pooled. Each experiment was performed at least five times. The differences in cell growth between culture conditions were highly significant. The asterisks indicate that values were significantly different from mean growth of B. burgdorferi in L15BS medium (P < 0.001, as determined by one-way analysis of variance with the Tukey-Kramer multiple-comparison post test). The difference between mean B. burgdorferi growth in coculture with tick cells and mean B. burgdorferi growth in BSK-H medium was also significant (P < 0.001).