Hyphae septate, hyaline. Conidiophores simple or branched. Phialides grouped in brush-like clusters (penicilli) at the ends of the conidiophores; conidia unicellular, round to ovoid, hyaline or pigmented, rough walled or smooth, in chains.


Surface: Texture velvety to powdery; Green, blue-green, gray-green, white, yellow, or pinkish on the surface.
Reverse: Usually white to yellowish, sometimes red or brown.
Growth Rate: Moderately rapid to rapid.
Note: If the isolate produces a red reverse and diffuse pigment in the agar, P. marneffei must be considered and the organism should be tested for thermal dimorphism; this is especially relevant if the patient has recently visited southeast Asia.


Penicillium is distinguished by its frequently greenish colonies and its branching or simple conidiophores supporting phialides in brush-like clusters known as penicilli. It is differentiated from Paecilomyces by its phialides lacking long, pointed apical extensions. In contrast to Scopulariopsis , its conidia lack a truncate base. P. marneffei produces downy gray-green colonies, often with a brownish or red tint caused by the presence of red or yellow pigmented sterile hyphae in the colony. The colonies, when incubated at 37 degrees C. on Sabouraud Dextrose Agar, characteristically lose this pigmentation and convert into yeast-like cells multiplying by fission. The diagnosis of infection due to P. marneffei rests on the histopathologic demonstration of cells multiplying by fission in the interior of leukocytes.


Penicillium are cosmopolitan, predominant in regions of temperate climate. Penicillia figure among the most common types of fungi isolated form the environment. Of the approximately 150 recognized species, some are frequently implicated in the deterioration of food products where they may produce mycotoxins. Other species are producers of penicillin. Infections with P. marneffei are primarily acquired in mountainous provinces of Northern Thailand, Laos, Myanmar, and Southeastern China.


Normally considered nonpathogenic with the exception of Penicillium marneffei , a dimorphic species capable of causing infection of the lymphatic system, the lungs, the liver, the skin, the spleen, and the bones. It has been known to cause keratitis (inflammation of the cornea), external ear, respiratory, and urinary tract infections, and endocarditis after insertion of valve prostheses.


Incubate at 25 degrees C. for 2-7 days.


1. Hensyl, William R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

2. St. Germain, Guy and Summerbell, Richard, Ph.D. 1996. Identifying Filamentous Fungi , 1st ed. Star Publishing Company, Belmont, CA.

3. Larone, Davise, H. 1995. Medically Important Fungi , A Guide to Identification , 3rd ed. American Society for Microbiology Press, Washington, D.C.

4. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.