Figure 1.

Study design. Invasion and replication of C. burnetii in bovine epithelial cell lines were quantified applying two different infection strategies differing in the time the inocula were left with the cells. Strategy B included a washing step after 1 day; in strategy A, inocula were not removed for the duration of the experiment. “Invasion B” refers to the quantitation of cell-associated C. burnetii genome equivalents (GE) 24 h after inoculation (values obtained in experimental setting B₂), “invasion A” to the quantitation of cell-associated GE after 7 days (values obtained in experimental setting A₃), each normalized to the GE numbers detected in the supernatant regained immediately after inoculation (time point “0 h”; values obtained in experimental settings A₁ and B₁). Thus the invasion was calculated as follows: (A) x = (A₃ × 100%)/A₁ and (B) x = (B₂ × 100%)/B₁. Replication efficiency was calculated as the fold-increase in the number of cell-associated GE from day 1 (values obtained in experimental setting A₂ and B₂) to values at day 7 (obtained in experimental setting A₃ and B₃). Thus the replication efficiency was calculated as follows: (A) = A₃/A₂ and (B) = B₃/B₂. Arrow depict sampling event, i.e. taking off the supernatant, washing the cell monolayer and detachment of the cells.