FIG. 1.
Effect of mutations of alpha-toxin on cytotoxicity. (A) Influence of mutations of alpha-toxin on death of epithelial cells. Monolayers of A549 cells (2 × 105 cells/well) were exposed by adding different concentrations of alpha-toxin (open squares), alpha-toxin-H35A (open circles), or alpha-toxin-H35L (solid triangles). Cell viability was determined by measuring LDH release 16 h after treatment and is expressed as an average of data from at least three experiments ± standard deviations. (B) Impact of mutations of alpha-toxin on its capacity to lyse sheep erythrocytes. The same amount of mutated toxins was added onto the blood agar plate, the plate was incubated overnight at 37°C, and hemolytic activity was observed. Lane 1, alpha-toxin (used as a positive control); lane 2, alpha-toxin-H35A; lane 3, alpha-toxin-H35L (used as a negative control) (22).