FIG 1.

T4519 promotes persistent intracellular survival and replication of Salmonella Typhi in a gentamicin protection assay. PMA (100 nM, 24 h)-differentiated THP-1 cells were infected with Ty2 or a mutant strain at an MOI of 10 for 1 h. Cells were washed repeatedly and were treated with gentamicin (100 μg/ml, 1 h) to remove extracellular bacteria. Intracellular bacteria were allowed to grow for the indicated times by culturing the cells in a gentamicin-containing medium (15 μg/ml). (A and B) CFU counts of intracellular bacteria recovered after lysis of the cells. The complemented Ty2Δt4519 strain is designated α-Ty2Δt4519. Error bars, means ± standard deviations for three independent experiments. ***, P < 0.001 (by Student's t test). (C) Cells were fixed and permeabilized, and intracellular bacteria were stained with polyclonal anti-Salmonella antisera, followed by an FITC-conjugated secondary antibody. The actin cytoskeleton was stained with rhodamine-phalloidin. Representative fluorescence microscopic images from multiple fields are shown in grayscale. (D) Trypan blue-negative cell counts by hemocytometer 24 h postinfection. (E) LDH was measured in the culture supernatants of the cells.