FIG. 4.
Internalization of M1 clinical isolates by lung epithelial A549 cells. Monolayers were infected with approximately 105 CFU of each culture. Internalized streptococci were determined by viable counts following 2 h of exposure to gentamicin and penicillin (22). Circles indicate M1inv+ strains. Stippled circles, M1inv+ strains isolated from patients with uncomplicated disease; triangles, M1inv− strains isolated from patients with uncomplicated pharyngitis. Strain 85-069 is M1inv− but harbors phage T13. Open circles and triangles represent strains whose genotypes were unknown to the investigator at the time of the experiment. NA, not available.