Electron microscopic studies on granules ofNocardia brasiliensisin man

Nocardia species: host-parasite relationships

The nocardiae are bacteria belonging to the aerobic actinomycetes. They are an important part of the normal soil microflora worldwide. The type species, Nocardia asteroides, and N. brasiliensis, N. farcinica, N. otitidiscaviarum, N. nova, and N. transvalensis cause a variety of diseases in both normal and immunocompromised humans and animals. The mechanisms of pathogenesis are complex, not fully understood, and include the capacity to evade or neutralize the myriad microbicidal activities of the host. The relative virulence of N. asteroides correlates with the ability to inhibit phagosome-lysosome fusion in phagocytes; to neutralize phagosomal acidification; to detoxify the microbicidal products of oxidative metabolism; to modify phagocyte function; to grow within phagocytic cells; and to attach to, penetrate, and grow within host cells. Both activated macrophages and immunologically specific T lymphocytes constitute the major mechanisms for host resistance to nocardial infection, whereas B lymphocytes and humoral immunity do not appear to be as important in protecting the host. Thus, the nocardiae are facultative intracellular pathogens that can persist within the host, probably in a cryptic form (L-form), for life. Silent invasion of brain cells by some Nocardia strains can induce neurodegeneration in experimental animals; however, the role of nocardiae in neurodegenerative diseases in humans needs to be investigated.

Mycetoma

We have reviewed the outstanding facts about mycetoma, including the history, first reports in India, the different causal agents according to their geographic distribution, mycologic characteristics, pathology, microbiology, behavior, evolution, immunology, experimental inoculations, associated bacterial complications, and osseous lesions. Various drugs available for treatment are mentioned and recommended. Therapeutic results depend on the age of the disease, and, above all, the bony involvement. N. brasiliensis mycetoma is one of the most frequent species and causes the greatest number of mycetoma cases in America, especially in Mexico.

Electron microscopy of radiating clubs in tonsillar crypts of swine

Tonsils of 25 adult swine with inflamed crypts were screened for the presence of radiating clubs, and five were selected for electron microscopic study of pathogenesis of clubs. Radiating clubs in crypts were surrounded by an exudate which principally contained neutrophils. Clubs were present on the outer surface of bacterial microcolonies; they also were present on the outer surface of plant particles wedged in crypts or on the cell walls of these particles near bacterial microcolonies. The study demonstrated development of clubs from an amorphous material derived from bacterial and leukocytic cells and also from precipitated proteins. The amorphous material was shaped into clubs by a protracted phagocytic activity of numerous neutrophilic leukocytes. The lesions with radiating clubs within crypts were not surrounded by granulomatous inflammation due to the intact epithelial lining of crypts, and therefore they differ from the granulomas having clubs around microbial colonies. They could, however, serve as models of pathogenesis of radiating clubs in the purulent core of specific granulomas with radiating clubs.

Morphology of the "sulphur granules" (Drusen) in some actinomycotic infections. A light and electron microscopic study

The granules (Drusen) within the inflammatory lesions in three cases of infection by Actinomyeetales were studied with light and electron microscopy. The material consisted of subcutaneous granulomas caused by Actinomyces bovis in a cow, epidural granulomas caused by A. viscosus in the spinal canal of a cat and cerebral granulomas caused by Nocardia in a dog.

The granules of A. bovis were 2000 to 3000 micrometers in diameter. Their centers consisted of a slightly basophilic, gram- and grocott-negative material with branching, gram-and grocott-positive filaments. The periphery was slightly basophilic or eosinophilic, but gram- and grocott-positive. Its surface was made of clubs (15 × 3.5 micrometers); they were acidophilic, gram- and grocott-negative. In the center of the granule there are numerous type a cells (coccobacillary cells with a trilaminar cell wall of 12 nanometers) and rarely type b cells (filaments with bilaminar cell wall of 30 nanometers). The periphery was made of germinative centers of type a cells. The clubs were lytic type b cells, embedded in an amorphous material.

The granules (Drusen) of A. viscosus were 200 to 600 micrometers in diameter. Their center was slightly eosinophilic, gram- and grocott-negative and contained gram- and grocott-positive filaments. Their periphery was basophilic and contained alternating gram-and grocott-negative areas and radial gram- and grocott-positive filaments. There were no clubs. In the center there were type b cells (filaments with a trilaminar cellular wall of 30 nanometers). The periphery was made of germinative centers of type a cells (coccobacillary with a trilaminar cell wall of 10 to 11 nanometers). The germinative centers were separated from each other by radial bundles of type b cells.

The granules (Drusen) of Nocardia were acidophilic, gram- and grocott-positive and surrounded by 1.8 × 0.5-micrometer clubs that were acidophilic, gram- and grocott-negative. There were type a cells (filamentous to bacillary with monolaminar cell wall of 19 nanometers and cross wall) and type b cells (filamentous to bacillary with monolaminar cell wall of 65 nanometers and without cross wall).

The remarkable morphological differences of the three species of Actinomycetales are specific, independent from host and type of tissue, and therefore reliable for diagnostic purposes.

An ultrastructural analysis of Nocardia during experimental infections in mice

Several strains of Nocardia that varied from virulent to avirulent were injected intraperitoneally into young mice. Histological and ultrastructural analysis of the resultant infections revealed that the bacteria and the lesions they induced were different depending upon the strain of organism used. Further, the morphological and tinctorial characteristics of the bacteria grown in vitro changes during growth in vivo. These observations strongly suggested that chemical and physical alterations occurred in the cell envelope of the Nocardia when grown in mice. Electron microscopy confirmed that significant structural modification occurred, especially in the cell envelope, when the nocardial cells established themselves within the host tissue. It was shown that the least virulent strain exhibited the most dramatic changes whereas the most virulent organism appeared to be affected the least.