FIG 3.

Carrier allele liaS^R135G decreases virulence in in vivo and ex vivo models of GAS disease. (A) Kaplan-Meier survival curve of mice (n = 15) after intramuscular infection with the parental invasive (red line) or mutant (blue line) strain. (B) The recovery of each bacterial strain (numbers of CFU) from mice (n = 20) at 72 h postinfection is plotted as the mean ± SEM. P values were determined by the Mann-Whitney U test. Red symbols, invasive strain; blue symbols, mutant strain. (C) Visual (top; 72 h postinoculation) and microscopic (bottom; 24 h postinoculation; magnification, ×4) inspection of mouse limbs. MGAS10870 caused a large necrotic lesion centered at the inoculation site (white box). Microscopic examination revealed extensive areas of necrosis (area with red outline) that breached fascial planes (black arrowheads) to cause severe muscle destruction with numerous nonviable (ghost) cells. MGAS10870liaS^R135G caused a comparatively smaller lesion (white box) with less severe fascial and muscle necrosis (area with blue outline). (D) Bactericidal assays of the parental invasive strain and the isoallelic mutant strain. (E) Bactericidal assays of the carrier strain [MGAS23431(liaS^R135G)] and the repaired mutant (MGAS23431liaS^WT). The error bars in panels D and E represent SEMs, and P values were determined by the t test (unequal variance).