INFECTION OF WHITE SWISS MICE WITH AIRBORNECRYPTOCOCCUS NEOFORMANS

Abstract

white Swiss male mice were allowed to run 3 days on previously sterilized soil that had been seeded with Cryptococcus neoformans 1 year previously. It was determined that the soil contained an average of 1.6 X 106 viable yeast cells per ml. The mice were observed for 24 weeks, at which time the survivors were necropsied. The total mortality rate during this period was 44%; 67% of the mice had positive cultures, including all who had a fatal infection. Two additional experiments were done with the same strain with the use of aerosols produced by a Henderson apparatus. In experiment 1, 39 mice received 11,000 viable cells each; in experiment 2, 40 mice received 14,622 viable cells. Both groups of mice showed similar mortality rates, with a total of 77% dead after 20 weeks in experiment 1, and 80% in experiment 2. All of the mice in experiment 1 had positive cultures, as did 95% of the mice in experiment 2.

Development of an Aerosol Model of Cryptococcus Reveals Humidity as an Important Factor Affecting the Viability of Cryptococcus during Aerosolization

“…Initial inoculum density was maximized to 1610 8 cells/mL in a 20 mL volume because the viability of Cryptococcus post-nebulization had not been previously determined, and yeast cells were larger (up to 10 mm) than typical aerosolized pathogens [55,59]. Our inoculum density is similar to previous reports used to initiate C. neoformans, Aspergillus, and bacterial aerosol infections, but our experiments utilized greater volume than previously reported [50,53,54,56,59]. The density of viable Cryptococcus yeast cells post-nebulization was equal to or greater than the inoculum density pre-nebulization.…”

“…Information extracted from the soil seeding infection was limited because infection rates and development of disease were variable, mice were exposed for multiple days, and the dosages of cells the mice were exposed to versus the dose initially retained in the lungs were not delineated. Infection initiated through the Henderson Chamber resulted in more consistent infection rates and development of disease in comparison to crude soil exposure [50]. Only 20% of mice exposed to aerosolized Cryptococcus basidiospores via a jet nebulizer succumbed to infection [53].…”

“…Current murine models are most frequently used but fall short of replicating the actual aerosol route of infection and may hinder our ability to decipher initial events that lead to the clearance or establishment of latent or progressive infection. Therefore these models may not accurately reflect the virulence properties of spores versus yeast, mating type a versus a strains, or the differences between molecular types or species [33,[49][50][51][52][53].…”

“…Aerosol infection models for Cryptococcus or other fungi have rarely been utilized [50,[53][54][55][56]. Historic applications of this approach include crude exposure from soil inoculated with Cryptococcus, utilization of a jet nebulizer, and infection in a Henderson Chamber [50,54,57]. Information extracted from the soil seeding infection was limited because infection rates and development of disease were variable, mice were exposed for multiple days, and the dosages of cells the mice were exposed to versus the dose initially retained in the lungs were not delineated.…”

“…Variable infection rates and disease development were likely due to differences in the inoculum used, method of aerosolization, duration of exposure, host genotype, and strain of Cryptococcus utilized. These early studies were successful at initiating infection, but computer-controlled facilities were not available, Cryptococcus species were not yet taxonomically differentiated, and mating and the production of spores versus yeast had not been fully appreciated [50,58].…”