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The comparative virulence of thermotolerant Mucorales was determined for cortisone-treated and untreated Swiss mice by intravenous administration of spores. The measure of virulence was based on an LD50 value, calculated after the 30-day observation period. Of the known etiological agents of mucormycosis, Mucor meihei, M. pusillus, Rhizopus arrhizus, R. chinensis, R. cohnii, R. microsporus, R. oryzae, R. rhizopodiformis and Cunninghamella elegans were able to produce fatal infections in mice; whereas, Mucor alternans, M. ramosissimus and Syncephalastrum racemosum were avirulent at dosages of up to 10(5) spores. Of those thermotolerant species which have not been reported to cause mucormycosis in human beings, Radiomyces embreei, R. spectabilis, Rhizopus oligosporus and Thermomucor indicae-seudaticae were found to produce fatal infections in mice; whereas, an isolate of Mycotypha africana was avirulent. Cortisone treatment of mice was found to lower their resistance to infection at a given spore dosage as measured by ET50 values.

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The contact sensitivity response of mice to dinitrofluorobenzene (DNFB), as determined by an epicutaneous painting and subsequent ear challenge assay, was enhanced by clindamycin administration. The optimal augmentation effect of clindamycin required its simultaneous administration at the time of DNFB skin sensitization. Clindamycin also was found to boost both in-vitro and in-vivo murine response to experimental infection with Candida lusitaniae. Intraperitoneal injection of 1-2 mg of the drug increased the clearance of yeast from organs after intravenous inoculation of mice. Clindamycin at concentrations of as low as 12.5 mg/l also increased the ability of cultured murine macrophages to kill the yeast without an increase in phagocytic activity.