Dermatophytes: Introduction, Infection and Its Laboratory Diagnosis


Introduction of Dermatophytes

Dermatophytes are a common label for a group of three types of fungi i.e. Trichophyton, Microsporum, and Epidermophyton that commonly cause skin, nail, and hair disease in our body.

Dermatophytes Infection

Dermatophytes are the causative agent of ringworm that infects only superficial keratinized tissues and infection of skin, hair, and nail.
They are a group of three genera.

a. Trichophyton ( skin, hair, and nail)
b. Microsporum (Hair and skin)
c. Epidermophyton (skin and nail)
Causative agents of ringworm do not involve in living tissue.
Spores of these fungi may live for a longer period in soil. Direct contact with soil causes us infection. It can also spread through contact with an infected person. The infection is commonly spread among children and by sharing items that may dirty.

They are keratinophilic fungi that infect keratinized tissues causing diseases known as dermatophytoses. Ringworm or tinea is synonyms for each other. It is a fungal infection of the skin. The name is “ringworm” but the infection is due to a fungus, not a worm.  The infection initially presents with red patches on affected areas of the skin and later spreads to other parts of the body. It can affect anyone. The infection may affect the skin of the scalp, groin, beard, feet, or other parts of the body.

Types Of Ringworm

Clinically ringworm is of the following types depending on the site of the body involvement-
e.g. Tinea axillaries: axilla
Tinea barbae: beard area
Tinea corporis: Non-hair skin
Tinea capitis: The hair and scalp of the body often appear as patches with the characteristic round “ring” shape.
Tinea corporis: in the groin
Tinea pedis: foot (Athlete’s foot)
Tinea pedis is common in people who go barefoot in public places where the infection can spread, for e.g. locker rooms, showers, swimming pools, etc.

 Laboratory Diagnosis of dermatophytes

Your dermatologist will diagnose ringworm due to dermatophytes by examining your skin and possibly using a black light to view your skin in the affected area. The fungus will fluoresce under black light. In case of infection, the areas of the skin where the fungus is located will glow. For confirmatory diagnosis your dermatologist will request the following  tests:

skin biopsy

fungal culture

Potassium Hydroxide(KOH) mount

Dermatophytes identification table
Trchophyton growth on DTM
Trichophyton colony onDTM
Trichophyton structures onLPCB
Trichophyton microconidia and macroconidia on LPCB
Microsporum colonial morphology
Microsporum growth
Microsporum spores
Microsporum structures
Epidermatophyton colonial morphlogy on DTM
Epidermatophyton growth
Epidermophyton structures on LPCB tease
Epidermophyton Macroconidia

Further Readings

  1. Medical Mycology. Editors:  Emmons and Binford, 2nd ed 1970, Publisher Lea and Febiger, Philadelphia.
  2. Rippon’s JW: Medical Microbiology. The pathogenic fungi and the Pathogenic Actinomycetes. 3rd ed 1988 Publisher WB Saunder co, Philadelphia.
  3. Clinical Microbiology Procedure Handbook Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
  4. A Text-Book of Medical Mycology. Editor: Jagdish Chander.  Publication Mehata, India.
  5.  Practical Laboratory Mycology. Editors: Koneman E.W. and G.D. Roberts, 3rd ed 1985, Publisher Williams and Wilkins, Baltimore.
  6. Topley & Wilsons Medical Mycology. Editors: M.T. Parker & L.H. Collier, 8th ed 1990, Publisher Edward Arnold publication, London.
  7. Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
  8. Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
  9. Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
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