Nocardia asteroides and Nocardia brasiliensis infections in mice

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Abstract
A model for N. asteroides and N. brasiliensis infections in Swiss white mice was established without the addition to the inocula of any form of adjuvant. Serial histopathological studies revealed that these 2 actinomycetes cause lesions that are quite different in their features. An acute suppurative abscess characterizes the lesions of N. asteroides. In the case of N. brasiliensis infections a granuloma is produced in which a striking feature is the presence of large numbers of foam-laden macrophages; occasional exceptions to this pattern were noted. EM demonstrated that these macrophages contain within their cytoplasm organisms in varying stages of degeneration. Repeated mortality studies in mice failed to demonstrate differences in mortality rates produced by N. asteroides and N. brasiliensis. Despite relatively trivial biochemical and antigenic differences between these 2 species of Nocardia, the local pathogenic response is quite different. The presence in the brasiliensis lesion of foamy macrophages with intracellular organisms is reminiscent of the histopathological features of lepromatous leprosy and of disseminated Mycobacterium bovis infection when this occurs in the immune suppressed situation. It is possible that N. brasiliensis infection produces a depression of cellular immunity that modifies the local host response to the organism.