Hyaline Hyphomyces Forming Conidia Singly

Scedosporium apiospermum

Formerly known as Monosporium apiospermum, S. apiospermum is the anamorph of Pseudallescheria boydii. Many authors consider this species a dematiaceous fungus (e.g. The ASM Manual of Clinical Microbiology 7th ed. and Larone's Medically Important Fungi: A Guide to Identification 3rd ed.) However, since Koneman et al. describe the species as hyalohyphomyces in their Color Atlas and Textbook of Diagnostic Microbiology, I've elected to describe it here with the hyaline hyphomyces for convenient cross-reference with that text.

Main cause of fungal mycetoma in North America; most often affects hands and feet but can form pulmonary fungus balls and infections at other sites
Agent of phaeohyphomycosis in developing countries
Now recognized as a medically important opportunistic fungus
Colonies grow rapidly, are cottony, and are smoky gray to dark brown; some laboratorians refer to a "house mouse gray" color; the reverse begins white but darkens as the colony matures
Conidiophores are hyaline and may be long or short
Conidiogenous cells are annellides
Conidia unicellular and obovate, truncate, single or in balls
Most isolates grow on cyclohexamide-containing media
May be confuse with the mold phase of Blastomyces dermatitidis

FIG. 1. Scedosporium apiospermum in slide culture.

Pseudallescheria boydii

Pseudallescheria boydii is the teleomorphic or sexual stage of Scedosporium apiospermum.

Causes mycetoma (maduramycosis)
Colonies mature moderately rapidly and are white and cottony, darkening with age; reverse is white initially but darkens to gray or black with maturity
Usually presents with tumor-like lesion yielding granular pus through a draining sinus
Growth is inhibited by cyclohexamide containing media
Forms large, brown cleistothecia that vary in diameter from 50-250μ and release elliptical ascospores
Cornmeal or potato dextrose agar may be useful in inducing the sexual stage of the fungus

Scedosporium inflatum

Also referred to as S. prolificans.

Causes invasive infection, usually arthritis or osteomyelitis; often resistant to antifungal agents
Colonies grow rapidly and are cottony, smokey gray to dark brown
Conidiophores hyaline and may be long or short
Conidiogenous cells annellides with prominent swollen bases and sharp angulation in conidiogenous cells ("crooked necks") appear between 5-7 days of incubation
Conidia unicellular, obovate, truncate, single or in balls; unlike S. apiospermum, does not have a known sexual stage
Most isolates fail to grow on media containing cyclohexamide

FIG. 1. Scedosporium inflatum in slide culture. Arrow indicate "crooked neck" characteristic of the organism.

FIG. 2. Scedosporium inflatum in slide culture.

Chrysosporium

Colonies grow moderately rapidly and vary in appearance
Usually considered a contaminant; may cause onychomycosis
Septate hyphae, 1-2 μ across
Conidia ovoid, 2-10 μ
Conidia broadly truncate base and broad basal scar carried singly and in short chains
May closely resemble Blastomyces dermatitidis

FIG. 1. Chrysosporium in slide culture. Conidia here are borne in short chains.

Sepedonium

Colonies waxy and white initially, but yellow with age; reverse is white
Generally considered a contaminant
May closely mimic the appearance of Histoplasma, but lacks microconidia and is not dimorphic (i.e. can't be converted to a yeast at 35-37°C)
Large, spherical, bluntly spiked macroconidia may be accompanied by smaller, ovate conidia borne singly from short conidiophores
Simple or branched conidiophores
Septate hyphae
May have cleistothecia

FIG. 1. Sepedonium in slide culture. Histoplasma is in the differential diagnosis here.

FIG. 2. Sepedonium cleistothecia in slide culture.

To examine other groups of hyalohyphomyces, follow the links below:

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