FIG 2.

The C. burnetii Δstmp1 mutant has a growth defect in macrophages and epithelial cells. (A) In axenic cultures, C. burnetii WT and Δstmp1 mutant bacteria have identical growth over 5 days, as determined by CFU assay for bacterial numbers. (B to D) However, the C. burnetii Δstmp1 mutant has a significant intracellular growth defect in (B) human monocyte-derived macrophages (hMDMs), (C) murine alveolar macrophages (MH-S), and (D) HeLa cells, as determined by CFU assay. Growth was calculated as the fold change over day 0 and shown as the mean ± standard error of the mean (SEM) from three separate growth experiments done in duplicate. Statistical significance was determined by multiple t tests or t test; ***, P < 0.005; ****, P < 0.001. (E and F) Immunofluorescence staining (E) and quantitative measurements (F) indicate that Δstmp1 CCVs are significantly smaller than WT or complemented Δstmp1 CCVs. Representative images of CCVs (arrows) stained by immunofluorescence at 6 dpi. Blue, DAPI (host cell nuclei); red, C. burnetii; green, LAMP1 (lysosomes and CCV). CCV size was measured using ImageJ, with each circle representing an individual CCV. Data are shown as the mean ± SEM of at least 20 cells in each of three independent experiments. Statistical significance was determined by one-way ANOVA with Tukey’s post hoc test.