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Diagnosis and pathogenesis of dermatophyte infections
1Department of Dermatology, University of Glasgow, UK.
Abstract:
Dissemination of dermatophyte fungi depends on direct or indirect contact between infected and uninfected hosts. The first step in the infection process is colonisation of the cornified surface of the stratum corneum. The fungal form which is the contagious and infectious particle is most likely to be the arthrospore or a hyphal fragment adhering to or contained within a corneocyte. It is the distinctive morphological forms of hyphae and arthrospores, and the relatively large size of dermatophytes in keratinous tissue, that provide the basis of a rapid diagnostic method using microscopy. Microscopy may also have to provide the definitive diagnosis of a dermatophyte infection, eg, in onychomycosis, where a significant proportion of the samples which are positive on microscopy fail to grow in culture. The sensitivity of microscopy can be enhanced using KOH that incorporates a variety of dyes, or a fluorescent brightener (eg, Calcofluor white or Blankophor BA). This type of agent can also be used to recognise fungal elements in biopsy sections. However, culture has certain benefits over microscopy; it is a more sensitive technique, since much more material can be examined and a definitive identity of the organism can be obtained.
Insights
Microscopy offers rapid diagnosis of dermatophyte infections by identifying fungal structures like hyphae and arthrospores. While culture is more sensitive for definitive identification, microscopy is crucial for diagnosing infections like onychomycosis.
Area of Science:
- Medical Mycology
- Diagnostic Microbiology
- Infectious Diseases
Background:
- Dermatophyte fungi spread through direct or indirect contact.
- Infection begins with colonization of the stratum corneum.
- Contagious fungal particles are likely arthrospores or hyphal fragments.
Purpose of the Study:
- To highlight the diagnostic utility of microscopy for dermatophyte infections.
- To compare microscopy with culture methods for fungal diagnosis.
- To discuss methods for enhancing microscopic sensitivity.
Main Methods:
- Microscopic examination of keratinous tissues for fungal elements (hyphae, arthrospores).
- Use of potassium hydroxide (KOH) with dyes or fluorescent brighteners to enhance visualization.
- Fungal culture for definitive identification and sensitivity comparison.
Main Results:
- Distinctive morphology and size of dermatophytes in keratin facilitate rapid diagnosis via microscopy.
- Microscopy can provide definitive diagnosis, especially in cases like onychomycosis where culture may fail.
- Enhanced microscopy (e.g., with Calcofluor white) improves detection in tissue and biopsy sections.
- Culture offers greater sensitivity by examining larger sample volumes and enabling definitive species identification.
Conclusions:
- Microscopy is a valuable rapid diagnostic tool for dermatophyte infections.
- Enhanced microscopy techniques improve fungal element detection.
- Culture remains essential for sensitive and definitive identification of dermatophytes.