Experimental Cerebral Zygomycosis in Alloxan-Diabetic Rabbits I. Relationship of Temperature Tolerance of Selected Zygomycetes to Pathogenicity

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Acute alloxan diabetic rabbits were used in a survey of the potential ability of Absidia, Cunninghamella, Mucor, Rhizopus, Syncephalastrum, and Thamnidium species to cause cerebral zygomycosis (phycomycosis, mucormycosis). Specifically, the correlation of thermotolerance with potential pathogenicity was studied. The test organisms fell into two groups: those able to grow well at 39 C on Sabouraud dextrose agar and those unable to grow at that temperature. Isolates unable to grow at 39 C were not pathogenic. The nonpathogens were C. elegans, M. jansenni, R. reflexus, R. stolonifer, and T. elegans. Two isolates of S. racemosum and one isolate of A. corymbifera, although able to grow well at 39 C in vitro, did not invade the brain or lungs of acutely diabetic rabbits. Three species of Rhizopus, R. chinensis, R. microsporus, and R. oligosporus, all of which grew at 39 C and which had not been previously known to cause cerebral zygomycosis, were as pathogenic as the only two previously implicated disease agents, R. arrhizus and R. oryzae. Studies were also carried out to determine whether animals inoculated with spores of selected zygomycetes many hours prior to the onset of acute diabetes would develop cerebral zygomycosis. Approximately 50% of the rabbits that became acutely diabetic 72 to 90 hr after receiving R. oryzae spores by nasal instillation succumbed to cerebral zygomycosis. Our study indicates that several members of the genus Rhizopus that grow well at 39 C or higher, other than R. arrhizus and R. oryzae, are potential etiological agents of cerebral zygomycosis.

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