Mitochondrial kinetics during mitosis in Cryptococcus neoformans--an ultrastructural study

Dormancy in Cryptococcus neoformans: 60 years of accumulating evidence

Cryptococcus neoformans is an opportunistic yeast that is present worldwide and interacts with various organisms. In humans, it is responsible for cryptococcosis, a deadly invasive fungal infection that represents around 220,000 cases per year worldwide. Starting from the natural history of the disease in humans, there is accumulating evidence on the capacity of this organism to enter dormancy. In response to the harsh host environment, the yeast is able to adapt dramatically and escape the vigilance of the host's immune cells to survive. Indeed, the yeast exposed to the host takes on pleiotropic phenotypes, enabling the generation of populations in heterogeneous states, including dormancy, to eventually survive at low metabolic cost and revive in favorable conditions. The concept of dormancy has been validated in C. neoformans from both epidemiological and genotyping data, and more recently from the biological point of view with the characterization of dormancy through the description of viable but nonculturable cells.

Correlation of in vitro activity and in vivo efficacy of itraconazole intravenous and oral solubilized formulations by testing Candida strains with various itraconazole susceptibilities in a murine invasive infection

OBJECTIVES

To examine whether in vitro antifungal susceptibility test results correlate with in vivo efficacy of two cyclodextrin-solubilized itraconazole formulations (intravenous and oral) against Candida in a murine model of invasive infection.

METHODS

A selected set of 12 Candida spp. strains with various itraconazole susceptibilities were tested. We studied the efficacy of intravenous and oral itraconazole administered once daily at dosages of 0.63, 2.5, 10 and 40 mg/kg body weight in mice lethally infected with each tested strain. Survival of mice in each treated group was monitored daily until the death of all control mice and compared between groups.

RESULTS

Survival of mice infected with 9 of 12 Candida strains with itraconazole MICs of ≤0.016-2.0 mg/L was significantly prolonged by treatment with intravenous itraconazole at dosages of 2.5 or 10 mg/kg and above. In contrast, the other three strains resistant to 8 mg/L itraconazole in vitro were refractory to the therapy, even at the highest itraconazole dosage (40 mg/kg). Closely similar in vivo data were obtained with the oral itraconazole therapy. The effective doses of the two itraconazole formulations increased with increasing itraconazole MICs for the infecting strains.

CONCLUSIONS

The in vivo efficacy of intravenous and oral itraconazole correlated with the in vitro susceptibility data.

Three-dimensional reconstruction of a pathogenic yeast Exophiala dermatitidis cell by freeze-substitution and serial sectioning electron microscopy

The structure of a budding cell of the pathogenic yeast Exophiala dermatitidis was observed in three dimensions after freeze-substitution, serial ultrathin sectioning and computer reconstruction. The nucleus occupied about 10% of the cell volume. The spindle pole body was composed of two disk elements connected by an intervening midpiece, and occupied about 0.01% of the cell volume. The cell wall consisted of an inner transparent layer, a middle electron-opaque layer, and an outer fibrous layer. The mitochondria occupied about 10% of the cell volume. There were numerous mitochondria in the mother cell and the bud, but no 'giant mitochondrion' was seen. The ratio of mitochondrial volume within the bud to the mitochondrial volume of the cell was close to the ratio of bud:cell cytoplasmic volume. The results emphasize the importance of good cryofixation for 'perfect' preservation of yeast cell structure.