KOH Wet Mount Preparation: Purpose, Principle, Procedure, Result Interpretation and uses

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Purpose: 

To identify fungi in clinical specimens such as hair, skin or nails.

Principle: 

The KOH mount is used to aid in detecting fungal elements in thick mucoid material or in specimens containing keratinous materials such as skin scales, nails and hair.  The KOH dissolves the background keratin, unmasking the fungus element to make them more apparent. This test cannot find out the exact species of fungi. It can only differentiate whether fungi is present or not and the basic fungal structure. Further tests must be performed to confirm the species of fungi.

Type of sample:

Sterile containers should be used for sample collection

  • Skin
  • Hair
  • Nail

Requirements:

Equipment

Light microscope (40X magnification)

Biological safety cabinet

Reagents

10% KOH (aqueous)

40% KOH (aqueous)

Cover slip 

Microscopic slides

Procedure for 10% KOH Preparation:

Measure the 10g of potassium hydroxide (KOH) pellets, the transfer to container.

Add 50ml distilled water; mix until the pellets is completely dissolved. Add remaining distilled water and make the volume 100ml. label the container and stored at room temperature.

Procedure:

Suspend fragments of skin scales, hair in a drop of 10% KOH and 40% KOH for nail.

Add a cover slip and let it incubate in room temperature for about half an hour.

The mount may be gently heated in flame of a Bunsen burner to accelerate the clearing process. Do not boil.

Examine under the microscope for fungal elements.

Quality control procedures:

Check the reliability of procedure with known species of ATCC Candida albicans 10231.

Result and Interpretation:

Positive: Appearance of fungal elements (Yeast cells with pseudohyphae, septate hyphae, Aseptate hyphae and branching).

Negative: No fungal elements seen.

Uses:

The KOH mount test is one of the main methods of diagnosing fungal infections. It is a primary screening tool for diagnosis of fungi, it’s used to visualize fungal elements bu may not identify the species of the fungi.

  

Fungal elements

References:

  1. Practical Medical Microbiology by Mackie & McCartney 14th Edition, Page No-796 – 798.
  2. Koneman’s Color Atlas and textbook of Diagnostic Microbiology, Sixth edition by Washington et. al., 2006Page No; 1151-1243.
  3. Bailey and Scott’s Diagnostic microbiology, 12th edition by Betty et al., 2007, Page no: 629- 717.

 

Read Also:

 India Ink Preparation

Modified Ziehl Neelsen Techniques


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