Taxonomy and ecological features
The causative agent of classic tinea pedis belongs to the genus Trichophyton. In microbiological nomenclature, this microorganism is identified as Trichophyton interdigitale. It is important to note that in mycological practice, it is also considered a specific variant of another well-known dermatophyte, namely T. mentagrophytes var. interdigitale.
From an ecological and epidemiological standpoint, this fungus is anthropophilic. This means that its natural reservoir and host is exclusively human, and transmission of the infection occurs via direct or indirect contact with infected individuals.
Clinical presentation and tissue tropism
The clinical manifestations of infection caused by Trichophyton interdigitale have a clear localization. The pathological process affects exclusively the lower extremities, forming the characteristic picture of mycosis.
Main targets of the pathogen:
- Nail plates: development of onychomycosis.
- Skin of the feet: involvement of the epidermis with various morphological elements.
On the skin of the feet, the infection manifests as a whole spectrum of pathological changes. Patients encounter the formation of vesicles, deep and superficial fissures, profuse scaling (scales), and erosions.
Key diagnostic feature: despite belonging to the genus Trichophyton, this particular species never infects hair. This is a crucial criterion for clinical differential diagnosis.
Laboratory diagnostic algorithm
Laboratory identification of the causative agent is based on two main stages: microscopy of native pathological material and study of the characteristics of the isolated pure culture.
1. Examination of pathological material For analysis, scrapings are usually taken from affected nail plates or skin scales are collected. Upon microscopic examination of these samples, the laboratory technician detects fungal elements in the tissues: mycelium and arthrospores.
2. Study of pure culture When culturing the pathogen on nutrient media, a colony grows, microscopic examination of which provides a detailed morphological picture. For Trichophyton interdigitale in pure culture, the following elements are characteristic:
- Thin, intensively branching mycelium divided by partitions (septate).
- Microconidia: have a characteristic pyriform (pear-like) shape, measuring from 2 to 3 µm.
- Macroconidia: larger structures, measuring approximately 5 × 25 µm.
- Presence of specific resting structures — chlamydoconidia.
Etiological structure of foot mycoses
Despite the fact that Trichophyton interdigitale is the classic causative agent of tinea pedis, the clinical picture of foot lesions can also be caused by other dermatophytes. To understand the general etiological structure, it is important to remember that similar foot lesions can be caused by two other significant pathogens:
- Trichophyton rubrum
- Epidermophyton floccosum
These three microorganisms form the basis of the etiology of fungal lesions of the lower extremities in modern clinical practice.
Briefly: answers to topical questions
On which selective nutrient media is the isolation of a pure culture of Trichophyton interdigitale performed?
Isolation of a pure culture of Trichophyton interdigitale is performed on Sabouraud agar, intended for the cultivation of fungi.
What antimycotic drugs are used for etiotropic therapy of tinea pedis?
Etiotropic therapy of tinea pedis is carried out with systemic and topical antimycotic drugs. The following drug groups are used for treatment:
- Griseofulvin and Terbinafine — systemic and topical drugs.
- Clotrimazole, Econazole, Miconazole, Ketoconazole — topical azoles.
- Naftifine and Butenafine — allylamines and other drugs.
Naftifine is a squalene epoxidase inhibitor and is used exclusively topically as a cream or gel twice a day.
To remember the clinical presentation of T. interdigitale: "Nails crumble, feet have fissures, and hair remains intact."
Class and exam questions
Can hair involvement be detected in a Trichophyton interdigitale infection?
No, this is excluded. One of the most important features of this pathogen is that it does not affect hair at all.
Which fungal elements are sought in skin scales and nail scrapings?
In native pathological material, laboratory technicians look for mycelial hyphae and arthrospores.
What do the microconidia of this fungus look like in pure culture?
Microconidia of Trichophyton interdigitale are pyriform in shape and small in size — about 2–3 µm.
What other fungi besides T. interdigitale cause foot mycoses?
In addition to it, the etiological agents of foot mycoses are often Trichophyton rubrum and Epidermophyton floccosum.
What else to study on this topic
- Mechanisms of formation of arthrospores and chlamydospores
- Differential diagnosis with Trichophyton rubrum
- Pathogenesis of vesicle and erosion formation on the skin of the feet
- Features of septate branched mycelium
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