Question
A strong alkali is used to make the causative organism to be visible more clearly in this preparation(shown in the image).Identify this preparation.
A. Gram’s stain.
B. India ink preparation.
C. KOH mount.
D. Hanging drop preparation.
Show Answer
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Correct Answer » C
Explanation
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Ans: C. KOH mount.
Potassium hydroxide (KOH) preparation
- It is used for the rapid detection of fungal elements in clinical specimen, as it clears the specimen making fungal elements more visible during direct microscopic examination.
- KOH is a strong alkali. When specimen such as skin, hair, nails or sputum is mixed with 20% KOH it softens, digests and clears the tissues (e.g., keratin present in skins) surrounding the fungi so that the hyphae and conidia (spores) of fungi can be seen under microscope
- KOH preparation is recommended in the following suspected conditions (this is not the exclusive lists);
| Suspected conditions |
Specimen |
Diagnostic characteristics |
| Aspergillus infection |
Sputum |
Septate hyphae with V-shaped branching |
| Dermatophytes (ringworm fungi) |
skin scrapings, nails or hair |
Septate hyphae or spherical yeast cells depending on the nature of etiologic agents involved. |
| Blastomyces dermatitidis infection |
Pus, sputum or skin specimens |
Yeast cells (large budding yeast cells with distinct broad base) of Blastomyces dermatitidis. B.dermatitidis is a dimorphic fungus with yeast cells in tissue. |
| Mucormycosis |
Exudates from infected lesions or tissue |
Aseptate hyphae of fungi causing mucormycosis. |
