FIG. 6.

Intracellular growth of S. pyogenes in A-549 cells. Confluent cell monolayers were infected with 5 × 10⁷ bacteria in 24-well plates. The cells were incubated for 90 min, washed, and incubated for another 1.5 to 4 h in medium containing 0.8 μg of penicillin per ml. GAS cell numbers were determined by serial dilution of cell lysates and plating on agar. Results are the means ± SEM of the numbers of GAS per well from four separate experiments; at each time point, triplicate samples were analyzed.