DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
RG-2 organism.
Morphological Description: Colonies are mostly flat to slightly raised, white to cream,
suede-like to downy, with either no reverse pigment or a yellow-brown to wine-red
reverse. Most cultures show scanty to moderate numbers of slender clavate to pyriform
microconidia. Macroconidia are usually absent, but when present are smooth, thinwalled
multiseptate, slender and cylindrical to cigar-shaped. Older cultures may show
numerous chlamydospores with a few clavate to pyriform microconidia.
Note: On primary isolation some cultures may lack reverse pigmentation and fail to
produce microconidia. These need to be subcultured onto media like lactritmel agar or
potato dextrose agar, which stimulate pigmentation and sporulation. If sporulation still
fails subculture the fungus onto Trichophyton agar No.1.
Confirmatory Tests:
Trichophyton rubrum (Castellani) Semon
Littman Oxgall Agar: Raised, greyish-white, suede-like to downy colony with no
reverse pigment. Some cultures may show a greenish-yellow diffusible pigment.
Lactritmel Agar: Flat, white to rose pink, downy to granular colonies with a deep winered
reverse pigment.
Sabouraud’s Dextrose Agar with 5% salt: Very stunted, white to cream, downy to
glabrous colony with a pale yellow-brown reverse pigment.
1% Peptone Agar: Flat, white to cream, downy to glabrous colony with no reverse
pigment.
BCP Agar: restricted colony growth and neutral (unchanged) pH. Colonies typically
demonstrate red pigment on reverse
Hydrolysis of Urea: Typically, negative at 7 days (some may be positive).
Vitamin Free Agar (Trichophyton Agar No.1): Good growth indicating no special
vitamin requirements. Colonies are flat, white to cream, suede-like to downy with a
deep wine-red reverse pigment.
Hair Perforation Test: Negative at 28 days.
Key Features: Include clinical history, culture characteristics, microscopic morphology
and failure to perforate hair in vitro.