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Penicillium marneffei on SDA

Penicillium marneffei  is showing grayish-pink  on SDA as shown above image.

Introduction and morphology of Penicillium marneffei on SDA

Penicillium marneffei exhibits thermal dimorphism by growing in living tissue or in culture at 37°C as a yeast-like fungus, and in culture at below 30°C as a mould. On SDA (without cycloheximide) at 25°C colonies are fast-growing, suedelike to downy, white with yellowish-green conidial heads. Colonies become grayish-pink to brown with age and produce a characteristic diffusible brownishred to wine-red pigment. Conidiophores are hyaline, smooth walled and bear terminal verticils or whorls of 3-5 metulae, each bearing 3-5 phialides. The conidiophores are described as biverticillate or irregularly monoverticillate. Conidia are globose to subglobose, 2-3 µm in diameter, smooth-walled and are produced in basipetal succession from the phialides.

Other biverticillate, red-pigment-producing Penicillium species include P. purpurogeum and P. rugulosa, from which these can be definitely differentiated by demonstration of dimorphism (mould to yeast conversion is achieved by subculturing on brain heart infusion agar (BHIA)at 37°C).
On BHIA at 37°C colonies are rough, glabrous, tan-colored and
yeast-like. Microscopically, the yeast cells are spherical to ellipsoidal, 2-6 µm in diameter, and divide by fission, rather than by budding. Numerous short hyphal elements and elongated sausage-shaped forms are also seen. Tissue sections show small, oval to elliptical yeast-like cells, 3 µm in diameter, either packed within histiocytes or macrophages, or scattered throughout the tissue. Occasional, large, elongated, sausage-shaped cells, up to 8 µm long with distinctive septa may be present. Tissue sections need to be stained by Gomori’s methenamine silver stain (GMS) stain to clearly see the yeast-like cells, which are often difficult to observe in hematoxylin and eosin stain preparations.

References

• Medical Mycology. Editors:  Emmons and Binford, 2nd ed 1970, Publisher Lea and Febiger, Philadelphia.
• Rippon’s JW: Medical Microbiology. The pathogenic fungi and the pathogenic Actinomycetes. 3^rd ed 1988 Publisher WB saunder co, Philadelphia.
• A Text Book of Medical Mycology. Editor: Jagdish Chandar.  Publication Mehata, India.
• file:///C:/Users/Berry/Pictures/B4416.pdf