Penicillium Species

ENVIRONMENTAL

Ubiquitous in nature, these fungi can be recovered from any location worldwide.

SEPTATE OPPORTUNISTS

Hyphae of most opportunists molds contain cross-walls. Those of medical importance fall into the phylum Deuteromycota. The septate opportunistic molds may be divided into those that are dematiaceous (dark-colored hyphae and/or conidia), and those that are hyaline (light colored hyphae and conidia). Organisms with dark hyphae on tease mounts also have dark green to black colonies, especially on the colony reverse. The colonial color aids in the initial identification. Hyaline organisms exhibit light-colored colonial aerial hyphae, but they may be covered over with brightly colored comidia; thus, a tease mount is required. In the following descriptions, key identifying features are capitalized.

HYALINE OPPORTUNISTS

Opportunists with light-colored hyphae may cause hyalohyphomycosis (infection caused by hyaline fungi).

PATHOGENICITY

Penicillium spp. rarely cause infections; most reports of disease involve chronic fungal sinusitis. Penicillium causes keratomycosis, penicilliosis, otomycosis, onychomycosis cilium causes keratomycosis, penicilliosis, otomycosis, onychomycosis, and rarely, deep infection. The only true pathogen in the genus. P. marneffei is a common cause of systemic infection in immunocompromised patients who have visited the endemic region of Southeast Asia. Penicillium marneffei causes a disseminated form of penicilliosis. This includes patients with AIDS or hematologic malignancies. Infections are usually disseminated, with multiple organ involvement. The fungus can be isolated from cutaneous lesions, which are frequently present in infected patients. Disseminated disease is typically fatal.

LABORATORY EVALUATION

Conidiophores are erect, sometimes branched, with metulae bearing one or several phialides on which oval to ovoid conidia are produced in long, loose chains. This commonly seen fungus is a rapid grower with colonies usually in shades of green or blue-green. Penicillium marneffei is unique among the Penicillium spp., being dimorphic. The yeastlike cells of P. marneffei can be detected in Wrightstained smears from skin lesions or bulk specimens. The cells of P. marneffei resemble those of H. capsulatum, oval to cylindric, measuring 3 to 6 μm long, and may have a cross wall. The mold form is described as having sparse green aerial and reddish brown vegetative hyphae and production of a red diffusible pigment. Polymerase chain reaction tests have been described for identification confirmation. Serologic in medical assays have shown to be important in early diagnosis; however, none are commercially available.

CULTURE

On SABHI agar at room temperature, the rapid-growing colony is initially velvety and white, later becoming powdery and BLUE GREEN with a white periphery and colorless reverse. Penicillium marneffei's culture on SABHI agar at room temperature, the rapid-growing, grayish floccose colonies have a finely wrinkled surface and a DARK RED pigment that diffuses out the agar. At 37°C, on blood agar, yeastlike colonies may appear in 3 to 4 days and are grayish white, waxy and attached to the agar surface.

MICROSCOPIC

The mycelium is septate. PENICILLI bear flask-shaped PHIALIDES, which in turn support CHAINS of round PHIALOCONIDIA. Conidiophores and phialoconidia may be hyaline to pigmented, and smooth to rough, depending on species. Penicillium marneffei's appears different microscopically. At room temperature, the septate mycelium is typical of Penicillium with conidiophores bearing up to five short broad METULAE (branched conidiophores) The WIDE PHIALIDES, which taper to narrow apices, are borne in groups of four to six on the metulae. Smooth, lemon-shaped PHIALOCONIDIA occur in chains. Growth at 37°C on blood agar is yeastlike; filamentous forms and yeast forms may be seen.