FIG. 3.

Colonial morphology of strain 64p following passage through human blood on nine consecutive occasions. A stationary culture of blood-passaged strain 64/bp9 was diluted in phosphate-buffered saline and spread on Todd-Hewitt agar. Following overnight incubation at 37°C, plates with ∼100 colonies were examined for colonial morphology. (A) Day 9 of blood passage demonstrating the presence of two colony types; (B) a small colony selected and expanded from the plate in panel A. The small-colony variants secreted an E64-inhibitable cysteine protease that led to hydrolysis of overlaid casein. (C) A large colony selected and expanded from the plate in panel A. The large-colony variants did not generate a cysteine protease.