Pathogenicity of Hansenula anomala in model of immunocompromised mice

Animal models: an important tool in mycology

Animal models of fungal infections are, and will remain, a key tool in the advancement of the medical mycology. Many different types of animal models of fungal infection have been developed, with murine models the most frequently used, for studies of pathogenesis, virulence, immunology, diagnosis, and therapy. The ability to control numerous variables in performing the model allows us to mimic human disease states and quantitatively monitor the course of the disease. However, no single model can answer all questions and different animal species or different routes of infection can show somewhat different results. Thus, the choice of which animal model to use must be made carefully, addressing issues of the type of human disease to mimic, the parameters to follow and collection of the appropriate data to answer those questions being asked. This review addresses a variety of uses for animal models in medical mycology. It focuses on the most clinically important diseases affecting humans and cites various examples of the different types of studies that have been performed. Overall, animal models of fungal infection will continue to be valuable tools in addressing questions concerning fungal infections and contribute to our deeper understanding of how these infections occur, progress and can be controlled and eliminated.

Nosocomial infection in newborns by Pichia anomala in a Brazilian intensive care unit

Disseminated candidiasis is the most common nosocomial fungal infection, and Candida albicans has been reported to account for 50% to more than 70% of cases of invasive candidiasis. However, recent reports have also suggested the emergence of infections caused by non-albicans species. In addition, less-common pathogenic yeasts (Malassezia, Trichosporon, Rhodotorula, Debaryomyces and Pichia) have recently been reported, with increased frequency, as causes of nosocomial infections with high mortality. This article describes two cases of fungemia caused by Pichia anomala in newborns that occurred in an intensive care unit (ICU), in November 2004 at the Instituto da Criança (Pediatric Institute) of the Hospital das Clínicas of the School of Medicine, São Paulo University, Brazil. The principal factors related to virulence (proteinase and phospholipase) and the susceptibility of the isolated strains to antifungal agents were also evaluated, and the biotype of each strain was determined through the use of an epidemiological marker (killer biotype).

Disruption of the Aspergillus fumigatus gene encoding nucleolar protein CgrA impairs thermotolerant growth and reduces virulence

Aspergillus fumigatus CgrA is the ortholog of a yeast nucleolar protein that functions in ribosome synthesis. To determine how CgrA contributes to the virulence of A. fumigatus, a Delta cgrA mutant was constructed by targeted gene disruption, and the mutant was reconstituted to wild type by homologous introduction of a functional cgrA gene. The Delta cgrA mutant had the same growth rate as the wild type at room temperature. However, when the cultures were incubated at 37 degrees C, a condition that increased the growth rate of the wild-type and reconstituted strains approximately threefold, the Delta cgrA mutant was unable to increase its growth rate. The absence of cgrA function caused a delay in both the onset and rate of germination at 37 degrees C but had little effect on germination at room temperature. The Delta cgrA mutant was significantly less virulent than the wild-type or reconstituted strain in immunosuppressed mice and was associated with smaller fungal colonies in lung tissue. However, this difference was less pronounced in a Drosophila infection model at 25 degrees C, which correlated with the comparable growth rates of the two strains at this temperature. To determine the intracellular localization of CgrA, the protein was tagged at the C terminus with green fluorescent protein, and costaining with propidium iodide revealed a predominantly nucleolar localization of the fusion protein in living hyphae. Together, these findings establish the intracellular localization of CgrA in A. fumigatus and demonstrate that cgrA is required for thermotolerant growth and wild-type virulence of the organism.

Pathogenicity of Cryptococcus neoformans var. gattii in an immunocompetent mouse model

The pathogenicity of two different genomic profiles of Cryptococcus neoformans var. gattii serotype B isolated from goats that died from cryptococcal pneumonia was assessed in an experimental model of immunocompetent mice. One strain of each randomly amplified polymorphic DNA (RAPD) profile (GR52 and GR56) and three reference C. neoformans isolates representing serotypes B, D and C were used. BALB/c male mice were inoculated by the intraperitoneal route with each strain. After 4 weeks of follow-up, the animals were sacrificed and autopsy specimens of testes, liver, spleen, kidney, lungs and brain were cultured and stained for histopathology. Although spontaneous mortality was only 2% (one animal), all mice except for those inoculated with serotype C showed positive cultures in almost one organ. The strain GR52 isolated from goat showed the highest rate of positive cultures (80%) followed by serotype D (77%). Serotype B reference strain and second goat strain GR56 were both isolated from 70% of samples. Serotype C was recovered in only 33% of organs, and never from brain or lung specimens. GR52 grew abundantly from all lung cultures, and yeast cells with large capsules were seen in histopathology inside the alveoli, peribronchial vessels and interalveolar spaces. They appeared to elicit no inflammatory response. We conclude that intraperitoneally inoculated C. neoformans var. gattii shows high virulence in this immunocompetent mouse model. Strain GR52 was highest in pathogenicity and had marked lung tropism. In contrast, the serotype C reference strain showed the lowest pathogenicity and seemed not to spread outside the abdominal viscera.