The contact system is activated on the bacterial surface after exposure to plasma, leading to antimicrobial activity. (A) S pyogenes AP1 bacteria were incubated in sodium citrate alone or in normal, fXII-, or fXIII-deficient plasma (all diluted 1:100 in sodium citrate) in the presence of ZnCl2, CaCl2, phospholipids, and the gold-labeled antibody against N-ϵ-γ-glutamyl-lysine for 15 minutes, and then analyzed by negative-staining electron microscopy. The scale bar indicates 100 nm. (B) S pyogenes AP1 bacteria were incubated in nonactivated or thrombin-activated normal and fXIII-deficient plasma (1:100 diluted). At the indicated time points, bacterial numbers were determined by plating of serial dilutions onto blood agar. Bacteria incubated in sodium citrate in the presence of thrombin served as controls. The data represent the means ± SD of 3 independent experiments. **P < .01; ***P < .001. (C) AP1 bacteria were incubated with normal or fXIII-deficient plasma and clotting was initiated by the addition of thrombin. Thin-sectioned clots before (0h) and after 1 hour (1h) of incubation at 37°C are shown. Similar amounts of dead bacteria (arrows) were detected in both samples after incubation. The scale bar indicates 1 μm.
