Question

Hair perforation test is positive for

• A. Trichophyton mentagrophytes
• B. Microsporum adouinii
• C. Epidermophyton floccosum
• D. Microsporum gypsum

Hint:

The hair perforation test is used classically to distinguish between two common Trichophyton species based on their ability to penetrate hair in vitro.

Answer 1

The Correct Option is A

Step 1: Understand the Hair Perforation Test. The hair perforation test (also called the hair perforation assay) is a mycological test used to differentiate dermatophytes. It is based on the ability of certain fungi to penetrate hair shafts and form wedge-shaped perforations perpendicular to the hair shaft.

Step 2: Procedure.

• Autoclaved blonde prepubital hairs are cut into small pieces and placed in 5 ml sterile distilled water.
• The test fungus is inoculated into the hair in the vial.
• Incubated at room temperature for up to 4 weeks.
• Individual hairs are examined microscopically in lactophenol cotton blue.

Step 3: Interpretation.

• Trichophyton mentagrophytes: Hair perforation test POSITIVE (forms wedge-shaped perforations in hair).
• Trichophyton rubrum: Hair perforation test NEGATIVE -- this is the key distinguishing feature between the two most common dermatophytes.
• Microsporum audouinii: Negative (does not perforate hair).
• Epidermophyton floccosum: Does not infect hair at all.
• Microsporum gypseum: Positive, but the question tests T. mentagrophytes as the classic answer.

Step 4: Conclusion. The hair perforation test is classically positive for Trichophyton mentagrophytes. This test is used specifically to differentiate T. mentagrophytes (positive) from T. rubrum (negative). Answer: Trichophyton mentagrophytes.