FIG. 1.

Gentamicin protection assays were initiated by infecting A431 cells with bacteria as noted (T = −13). After 12 h of infection cultures were incubated with gentamicin for 1 h. They were then rinsed thoroughly and incubated further without gentamicin (T = 0). At various times, cells were disrupted, and intracellular bacteria were quantified as described in Materials and Methods. Desferal or ferric nitrate was added to some cultures after gentamicin removal (T = 0). Some mutants required ferric nitrate to promote growth during the invasion phase of the assay (T = −13 to −1).