The ability of B. melitensis 16 M at different phases of growth to invade HeLa cells. (A) Growth curve of B. melitensis 16 M grown overnight in tubes with loose lids and shaking in F12K cell culture medium supplemented with 10% (v/v) HI-FBS. Results are the average +/- SD of 3 independent experiments. Mid-log, late-log and stationary growth phases are marked with *. (B) HeLa cell infections were performed at MOI 1,000:1 for 30 min. The intracellular number of late-log growth phase cultures of B. melitensis was significantly different from those grown to mid-log (* = P < 0.05) and stationary (** = P < 0.01) growth phases. Results are presented as the number of CFU from internalized bacteria 30 min post-infection per 103 cells inoculated. Data presented are the mean +/- SD (error bars) of triplicate samples from 3 independent experiments.