Infectious Agents
Case 1

Light Microscopy
Electron Microscopy
Discussion

Case 1
Case 2
Case 3
Case 4

Electron Microscopy of Infectious Agents

Case I: Pneumocystis carinii

Discussion:

Pneumocystis carinii is an opportunistic organism which infects patients with diminished immune systems. Although the exact nature of the organism is not known, it is considered to be a protozoan. Specimens suspected to be infected are generally not sent for electron microscopic evaluation because the organisms are readily demonstrated with silver methenamine and H&E staining.

The ultrastructural features of Pneumocystis carinii have been well documented in the literature (1) and related to the life cycle (2) of the organism. The larger cysts may be collapsed into crescent shapes, and preservation may be sub-optimal due to poor penetration of fixative through the cyst wall. The primary role for electron microscopic evaluation is to demonstrate the filopodial extensions of the cell wall, or to identify the organism in those instances in which the infection is equivocal by routine cytological or histopathologic methodologies.

References:

1. Huang, S-N., and Marshall, K.G.: Pneumocystis carinii infection. A cytological, histologic, and electron microscopic study of the organism. Am. Rev. Resp. Dis. 102:623-635, 1970.
   
2. Barton, E.G., and Campbell, W.G.: Pneumocystis carinii in lungs of ratstreated with cortisone acetate. Ultrastructural observations relating to the life cycle. Am. J. Pathol. 54:209-236, 1969.

Case 1

Case 2

Case 3

Case 4