Page 128 - LECTURE NOTES

the auto fluorescence of keratin (dull blue) or the fluorescence of creams and ointments

that may have been applied to the lesion.

5.5.4. Immunology and serology
The immunological aspects of “ringworm” are incompletely understood. It is clear that a

primary infection produces partial local immunity to reinfection but this protection varies
in duration and extent depending on the host, the site of infection and the species of

Dermatophytes. Cutaneous hypersensitivity (immediate and/or delayed) may occur and

circulating antibodies have been detected in infected individuals but neither
phenomenon has been shown to be of any diagnostic value.

5.5.5. Fungal Culture
Dermatophytes develop well on culture media containing an organic source of nitrogen.

Those commonly used for isolations are 4% malt extract and Saboraud’s dextrose agar.
It is usual to add chloramphenicol to these media and reduce bacterial growth.

Inoculation of an adequate number (>10) of small (<1 mm) fragments of the specimen

should be made. Although many dermatophytes may develop recognizable colonies
0
with in 5-7 days, cultures should be retained for at least 3 weeks at 25-30 C and longer
at lower temperatures before making a final diagnosis. Either Petri dish or test tube

culture is satisfactory and there is little risk of laboratory infection.

Dermatophyte isolates can usually be distinguished from contaminants by the
occurrence of compact growth around the inocula and the color of the colony

Dermatophytes are never green, blue or black.

5.6. Viruses

Vesicles are cleaned with 70% alcohol followed by sterile saline. Viruses are obtained

by unroofing a vesicle with a needle or a scalpel blade. The fluid is collected with a
swab or with a tuberculin syringe with a 26 to 27-gauge needle.

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