Penicillium marneffei

WARNING: RG-3 organism. Cultures of Penicillium marneffei may represent a biohazard to laboratory personnel and should be handled with caution in an appropriate pathogen handling cabinet. P. marneffei exhibits thermal dimorphism and is endemic in Southeast Asia and the southern region of China.

On Sabouraud's dextrose agar at 25C, colonies are fast growing, suede-like to downy, white with yellowish-green conidial heads. Colonies become greyish-pink to brown with age and produce a diffusible brownish-red to wine red-pigment. Conidiophores are hyaline, smooth-walled and bear terminal verticils of 3 to 5 metulae, each bearing 3 to 7 phialides. Conidia are globose to subglobose, 2 to 3 um in diameter, smooth-walled and are produced in basipetal succession from the phialides.

On brain heart infusion (BHI) blood agar incubated at 37C, colonies are rough, glabrous, tan-colored and yeast-like. Microscopically, yeast-cells are spherical to ellipsoidal, 2 to 6 um in diameter, and divide by fission rather than budding. Numerous short hyphal elements are also present.

Culture of P. marneffei showing distinctive red diffusable pigment.

Phialides and conidia of P. marneffei.

Clinical significance:

Penicillium marneffei exhibits thermal dimorphism by growing in living tissue or in culture at 37C as a yeast-like fungus or in culture at temperatures below 30C as a mould. This fungus has been isolated from bamboo rats and is endemic in Southeast Asia and the southern region of China. Over 30 cases of hyalohyphomycosis cause by P. marneffei, especially in AIDS patients have now been reported.

Mycosis: Penicilliosis marneffei

Further reading:

Kwon-Chung, K.J. and J.E. Bennett. 1992. Medical Mycology. Lea & Febiger, Philadelphia and London.