FIG. 3.

S. pyogenes is virulent in zebrafish embryos but, as in adult zebrafish, the SLS⁻ mutant is not as virulent. (A) Yolk sac injections. The site of injection of 1 × 10⁵ CFU of wild-type (WT) S. pyogenes, the SLS⁻ mutant, or PBS alone (Ctrl) in the yolk sac is indicated by the arrow. The diagram was adapted from Kimmel et al. (39) with permission of the publisher, John Wiley & Sons, Inc. (B) Analysis of virulence. The survival data of injected embryos are presented as a Kaplan-Meier plot. Infected embryos were examined for viability every 2 h by microscopy. Data shown are pooled from three independent experiments using 15 embryos per group. These data show that the SLS⁻ mutant is significantly attenuated (P < 0.011). (C) Infected embryos were sacrificed every 30 min during the first 6 h of infection for assessment of the number of CFU. Groups of five embryos each were examined at each time point for each strain analyzed. The data shown represent the mean and standard deviation of three independent experiments. There was no significant difference between groups.