FIG. 5.

Invasion kinetics of the wild-type strains (A-20 and NZ131) and isogenic mutants (SW507 and SW510). Confluent cell monolayers were infected with 5 × 10⁷ bacteria in 24-well plates. The cells were incubated for 1.5, 2, 3, 4, 5, and 10 h, washed with PBS, and incubated for another 1.5 h in medium containing 0.8 μg of penicillin per ml. GAS cell numbers were determined by serial dilutions of cell lysates and plating on agar. Results are means ± standard errors of the means (SEM) of the numbers of GAS per well from four separate experiments; at each time point, triplicate samples were analyzed.