Collecting Skin Scrapings for Fungal KOH Exam
Select a scaly lesion
Use sterile #15 blade or glass slide to take skin scrapings from representative lesion
Scrape the skin scales into a single compact pile
Add 1 drop of 10-20% KOH Solution or Chlorazol Black E, cover with cover slip
Heat gently over butane burner, not alcohol flame, avoid boiling
A fungal culture
____ can determine which type of fungus is present. Since fungi generally grow slowly, it can take 2- 4 weeks for a ____ to produce test results.
A few culture mediums are available for dermatophyte growth.
Sabouraud agar containing neopeptone or polypeptone agar and glucose is often used for fungal culture. However, it does not contain antibiotics and may allow overgrowth of ____ and bacterial contaminants.
Mycosel, a commonly used agar, is similar to Sabouraud agar but has antibiotics.
Commonly, dermatophyte test medium (DTM) is used. It contains antibacterial (ie, gentamicin, chlortetracycline) and antifungal (ie, cycloheximide) solutions in a nutrient agar base. This combination isolates dermatophytes while suppressing other fungal and bacterial species that may contaminate the culture
Following culture inoculation, potential fungal growth is monitored at 2 weeks and 4 weeks.
Positive culture results vary depending on the medium used.
DTM contains phenol red solution, which causes a color change from straw-yellow to bright-red under alkaline conditions, indicating a positive dermatophyte culture result. However, the color makes identification of culture morphology (particularly pigmentation) difficult.
Sabouraud or Mycosel agar should be used to assess gross and microscopic colony characteristics.
Sterile cotton swab or #15 blade
Place scales on proper ____ media
DTM, Sabouraud or Nickerson's Media
Incubate at room temperature for 4 weeks, read culture at 2 and 4 weeks
Must be CLIA approved lab