Electron Microscopy of the Phagocytosis of Capsulated Bacillus anthracis.

The phagocytosis of capsulated vegetative cells of Bacillus anthracis in the mouse spleen was studied by thin sectioning techniques of electron microscopy. Mice were injected with autoclaved suspensions of capsulated and noncapsulated vegetative cells via the tail vein. The animals were killed 5, 10, and 30 min and 4 hr postinjection, with the central portion of the spleen being removed and procssed for electron microscopy. Fixation was with 2% KMnO(4) for 2 hr. Results of this study indicated that phagocytosis of autoclaved, capsulated anthrax bacilli was through the normal phagocytic process. The vesicular membrane or phagosome membrane was still present around these killed, capsulated organisms 4 hr postinjection. It is concluded that such cells possess no toxic principle to account for the supposed destruction of the phagosome membrane previously reported.