Scanning electron microscopy of Acanthamoeba culbertsoni as observed in the subarachnoid space

Scanning electron microscopy was used to study the pathogenic protozoan, Acanthamoeba culbertsoni, in the leptomeningeal subarachnoid space surrounding the spinal cord of the experimentally inoculated dog. Know to inhabit such areas as moist soils, stagnant waters, and sewage around the world, these protozoans have been identified as etiologic agents in numerous cases of meningoencephalitis. Infection occurs via a nasopharyngeal inoculation, through penetration of the olfactory mucosal epithelium and cribriform plate, into the subarachnoid space, whence it gains access to the central nervous system. Stock preparations of these amebae extracted directly from their culture medium for scanning microscopic study provided an index for their identification within the subarachnoid space and also permitted a heretofore unobserved survey of their pleomorphic surface features. From the observations of others, it had appeared that the ultimate portal of entry into the central nervous system involved some type of cytolytic process; however, this study illustrates an action of simple diapedesis in which the organisms seek a pathway of least resistance; namely the naturally-occurring pial fenestrations.