Ultrastructural observations in cat scratch disease.

Because the causative bacterium of cat scratch disease has not been definitively cultured or fully characterized, the authors have studied its ultrastructure in lymph node biopsies from two patients using glutaraldehyde-fixed tissue. In both specimens, the organisms were invariably extracellular, forming small groups within bundles of collagen fibrils. Their appearance was similar in necrotic and viable regions of the nodes, although in the latter sites they could not be identified by light microscopic examination with the Warthin-Starry stain. The bacteria were pleomorphic rods, and, despite faint gram-negative staining, their walls were consistently thick and homogeneous.