FIG 4.

Deletion of the pilus backbone gene in MGAS10870 liaS^R135G partially restores virulence and reverses the carrier phenotype. (A) Kaplan-Meier survival curve of mice following intramuscular infection with MGAS10870 (parental strain), MGAS10870 Δtee3 (parental strain, pilus negative), MGAS10870 liaS^R135G (carrier mutant), or MGAS10870 liaS^R135G Δtee3 (carrier mutant, pilus negative). *, P < 0.05 (log-rank test) relative to both the pilus-positive and pilus-negative carrier mutant. (B) Visual inspection and histopathology of infected mouse limbs at 72 and 24 h postinfection, respectively. (Top row) White boxes, areas of abscess-like formation centered at the inoculation site of the limbs; (bottom row) white arrowheads, areas of marked neutrophil infiltration and necrotic fascial and muscle tissue that extend beyond the border of the field of view; black oval, a well-circumscribed abscess that is limited to the fascial plane and surrounded by healthy muscle tissue (magnification, ×4). (C) Pathology score for wild-type, isogenic carrier, and pilus-negative derivatives based on microscopic examination at 24 h postinfection. *, P < 0.05 (Wilcoxon rank sum) compared to all other strains.