FIG. 3.

Bacterial invasion and persistence within mammalian cells. S. aureus strains were incubated with MAC-T cells for 90 min to allow invasion. Cell monolayers were then washed, and lysostaphin was added to the medium to kill extracellular bacteria. Adherent eucaryotic cells were incubated for a total of 24 h in the presence of lysostaphin. Persistent intracellular bacteria were then quantified after eukaryotic cells were washed and lysed. Values on the graph indicate the relative percentages of the initial inoculum found within cells for each strain, and these were compared to that obtained for S. aureus Newbould (100%). Standard deviations and statistical significance compared to the corresponding S. aureus Newbould results are indicated (*, P < 0.05; **, P < 0.01; ***, P < 0.001).