Plaque forming, invasion efficiencies and net intracellular survival and replication of <i>B</i>. <i>pseudomallei</i> wild-type and its derivative strains.

<p>(A) Plaque forming and (B) invasion efficiencies of <i>B</i>. <i>pseudomallei</i> K96243 wild-type, 6H4 mutant or 6H4/pME1039 complemented strains in infect HeLa cells. Plaque-forming efficiency was calculated as: number of plaques/bacterial CFU added per well. Percent invasion was determined as: (number of intracellular bacteria post infection/number of CFU added) × 100. <i>B</i>. <i>pseudomallei</i> K96243 wild-type (black bar), 6H4 mutant (white bar) and the 6H4/pME1039 complemented (checked bar) strains were used to infect (C) HeLa and (D) J774A.1 macrophage cells. Intracellular loads of bacteria were enumerated at 4, 6, 8, and 24 h p.i. Asterisks indicate significant differences (<i>P</i> < 0.05, <i>t</i>-test) between wild-type and its derivative strains. Results are presented as standard errors of the means for experiments done in triplicate, with three independent experiments.