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The comparative virulence of thermotolerant Mucorales species in mice
Abstract:
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.
Insights
This study determined the virulence of thermotolerant Mucorales in mice, identifying several species capable of causing fatal infections. Cortisone treatment reduced mouse resistance, highlighting its role in mucormycosis susceptibility.
Area of Science:
- Mycology
- Infectious Diseases
- Toxicology
Background:
- Mucormycosis is a serious fungal infection caused by Mucorales.
- Understanding the virulence of different species is crucial for risk assessment.
- Thermotolerant Mucorales are of particular interest due to their growth conditions.
Purpose of the Study:
- To comparatively assess the virulence of various thermotolerant Mucorales species in a murine model.
- To evaluate the impact of cortisone immunosuppression on susceptibility to these fungi.
Main Methods:
- Intravenous administration of fungal spores to cortisone-treated and untreated Swiss mice.
- Determination of lethal dose 50 (LD50) values over a 30-day observation period.
- Calculation of effective time 50 (ET50) values to assess resistance changes.
Main Results:
- Several known mucormycosis agents (e.g., Rhizopus arrhizus, Mucor pusillus) were virulent in mice.
- Newly identified virulent species include Radiomyces embreei and Thermomucor indicae-seudaticae.
- Cortisone treatment significantly lowered mouse resistance to fungal infections.
Conclusions:
- The study identified specific thermotolerant Mucorales species with significant virulence in mice.
- Cortisone immunosuppression exacerbates susceptibility to mucormycosis.
- Findings contribute to understanding the pathogenic potential of these fungi.