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Abstract

Penicillium marneffei is a dimorphic pathogenic fungus responsible for opportunistic infection in HIV infected individuals. The fungus displays dimorphic switching in response to temperature changes. At 25°C, it grows in mold form that produces penicilli conidia which are thought to be infectious. At 37°C, the fungus transforms into a fission yeast. To investigate this morphological conversion, P. marneffei conidia were grown in media supplemented with various organic substances. Sabouraud dextrose broth (SDB) supplemented with 4% yeast extract enhanced regular fission yeast production, whereas SDB alone and SDB supplemented with fetal bovine serum did not produce homogeneous cultures. The fungus in Sabouraud maltose broth exhibited filamentous hyphae, while its growth in Sabouraud galactose broth was inhibited. Yeast nitrogen base (YNB) medium supplemented with glucose gave hyphal growth and supplemented with N-acetylglucosamine (GlcNAc) gave retarded growth with multiseptate hyphae. Conidia-yeast conversion was not observed in YNB supplemented with glucose plus various amino acids. However, when 1% peptone was added to these YNB media, however, yeast cells or short multi-septate hyphae were produced. Surprisingly, conidia cultivated in distilled water containing 1% peptone gave uniform fission yeast similar to yeast cells found in clinical specimens. Thus, 1% peptone supplementation was responsible for the yeast transition and will serve as simple method to obtain pure P. marneffei yeasts for future studies on virulence, invasiveness, and pathogenesis.