Entrapment and immobilization of S pyogenes inside the clot. Scanning electron micrographs showing the structure of clots generated from normal plasma (A,C,E) or fXIII-deficient plasma (B,D,F) in the absence (A-B) or presence (C-F) of bacteria. The scale bars indicate 10 μm in panels A through D and 1 μm in panels E and F. The transmission electron micrographs depict S pyogenes alone (G), after exposure to thrombin-activated plasma (H), and after exposure to plasma followed by immunostaining with a gold-labeled N-ϵ-γ-glutamyl-lysine antibody recognizing the fXIII cross-linking site (I). Scale bars indicate 1 μm in panels G and H and 100 nm in panel I.