FIG. 7.

SEM and Gram staining reveals GAS biofilms embedded within the macroscopic structures recovered from MGAS5005 Δsrv ΔspeB-infected middle ears. (A) Middle ear chamber of a euthanized chinchilla infected with MGAS5005 Δsrv ΔspeB filled with a visible macroscopic structure (black arrow). (B) SEM of a representative 2 dpi macroscopic structure. Notice the clustering of chains of cocci into microcolonies (white arrow). (C) H&E staining (left column) and Gram staining (right column) of sections from two representative 7 dpi macroscopic structures. Notice the presence of host fibrin and numerous Gram-positive microcolonies (white and black arrows). Magnification, ×20.