FIG. 4.

Intracellular replication of parental B. abortus 2308 and virB1 polar mutant strain in HeLa cells. Monolayers of HeLa cells were inoculated with 5 × 10⁷ CFU of bacteria. After 1 h of incubation at 37°C, cells were washed as described in the text and streptomycin and gentamicin were added. CFU were determined at the indicated times. Each determination is the average of two independent experiments performed in duplicate. In all cases, the standard error of each mean was less than 5%. ●, B. abortus 2308; ○, B. abortus 2308 virB1::Kan; ⧫, B. abortus 2308 virB1::Km(pVK8.3); ◊, B. abortus 2308 virB1::Km(pBBR4-virB1).