Treatment of documented and suspected neutropenia-associated invasive fungal infections

Cell-type-specific transcriptional profiles of the dimorphic pathogen Penicillium marneffei reflect distinct reproductive, morphological, and environmental demands

Penicillium marneffei is an opportunistic human pathogen endemic to Southeast Asia. At 25° P. marneffei grows in a filamentous hyphal form and can undergo asexual development (conidiation) to produce spores (conidia), the infectious agent. At 37° P. marneffei grows in the pathogenic yeast cell form that replicates by fission. Switching between these growth forms, known as dimorphic switching, is dependent on temperature. To understand the process of dimorphic switching and the physiological capacity of the different cell types, two microarray-based profiling experiments covering approximately 42% of the genome were performed. The first experiment compared cells from the hyphal, yeast, and conidiation phases to identify "phase or cell-state-specific" gene expression. The second experiment examined gene expression during the dimorphic switch from one morphological state to another. The data identified a variety of differentially expressed genes that have been organized into metabolic clusters based on predicted function and expression patterns. In particular, C-14 sterol reductase-encoding gene ergM of the ergosterol biosynthesis pathway showed high-level expression throughout yeast morphogenesis compared to hyphal. Deletion of ergM resulted in severe growth defects with increased sensitivity to azole-type antifungal agents but not amphotericin B. The data defined gene classes based on spatio-temporal expression such as those expressed early in the dimorphic switch but not in the terminal cell types and those expressed late. Such classifications have been helpful in linking a given gene of interest to its expression pattern throughout the P. marneffei dimorphic life cycle and its likely role in pathogenicity.

Comparative therapeutic efficacy of a novel lyophilized amphotericin B lecithin-based oil–water microemulsion and deoxycholate-amphotericin B in immunocompetent and neutropenic mice infected with Candida albicans

The in vivo efficacy of a new amphotericin B (AmB) oil-in-water lecithin-based microemulsion delivery system (M-AmB) compared to deoxycholate-AmB (D-AmB) was studied in an immunocompetent and neutropenic murine model of systemic candidiasis. D-AmB was administered at the maximum tolerated dose of 1 mg/kg whereas M-AmB was given at the doses of 1, 2 and 3 mg/kg; doses were well tolerated due to their reduced toxicity. Both formulations were administered 24, 48 and 72 h after infection in immunocompetent mice, and 2, 6 and 24 h after infection in neutropenic mice. Kaplan-Meier survival curves showed that the M-AmB treated group had a better survival time than infected mice without treatment used as a control group (P = 4.66 x 10(-6)), and the Mann-Whitney W statistical test indicated that it reduced the percentage of mortality and fungal load in the most representative organs. This new formulation is a designed competitor which has proved to present better results than D-AmB in an established infection not only in immunocompetent but in neutropenic mice as well.

Identifying phase-specific genes in the fungal pathogen Histoplasma capsulatum using a genomic shotgun microarray

A fundamental feature of the fungal pathogen Histoplasma capsulatum is its ability to shift from a mycelial phase in the soil to a yeast phase in its human host. Each form plays a critical role in infection and disease, but little is understood about how these two morphologic phases are established and maintained. To identify phase-regulated genes of H. capsulatum, we carried out expression analyses by using a genomic shotgun microarray representing approximately one-third of the genome, and identified 500 clones that were differentially expressed. Genes induced in the mycelial phase included several involved in conidiation, cell polarity, and melanin production in other organisms. Genes induced in the yeast phase included several involved in sulfur metabolism, extending previous observations that sulfur metabolism influences morphology in H. capsulatum. Other genes with increased expression in the yeast phase were implicated in nutrient acquisition and cell cycle regulation. Unexpectedly, differential regulation of the site of transcript initiation was also observed in the two phases. These findings identify genes that may determine some of the major characteristics of the mycelial and yeast phases.