F4 Superficial Fungi

Classification of Fungi

Tissue Distribution

Classification of fungi is primarily based on the area of infection and the types of tissues they affect. These classifications consider the most common portals of entry for the fungi and the immediate sites where they establish their infections.

5 Classifications of Fungi:

  1. Superficial: Fungi that reside on the outermost layers of the skin without penetrating deeper tissues.

  2. Cutaneous: Fungi that affect the outer layers of skin, hair, and nails, typically thriving on keratin.

  3. Subcutaneous: Fungi that invade deeper tissues, often as a result of skin trauma. These can lead to severe localized infections.

  4. Endemic (Primary/Systemic): Fungi commonly found in specific geographical areas that can infect otherwise healthy individuals.

  5. Opportunistic: Fungi that cause infections primarily in individuals with weakened immune systems or underlying health conditions.

Mycoses:

Refers to infections caused by fungi, which can range from superficial to life-threatening systemic infections.

Superficial Fungi

Superficial fungi reside on the outer layers of the body, including the skin and hair without infiltrating deeper tissues. Their clinical manifestations are primarily external.

Cellular Response:

The immune system's response is typically minimal unless the fungi penetrate deeper layers of skin.

Main Sites of Infection:

  • Skin: Bacteria and fungi primarily infect the outer surface.

  • Hair: Fungi can infect hair follicles but do not reach the scalp.

Surface Level Infections:

Common examples include Pityriasis versicolor which causes skin discoloration, and Tinea nigra which affects the palms and soles. For hair, Black piedra and White piedra are significant infections.

Transmission:

Superficial fungi are often transmitted through:

  • Person-to-person contact: Direct transfer of spores from one person to another.

  • Contaminated clothing and garments: Clothing can harbor spores that infect the new host.

Specific Genus and Species for Superficial Fungi:

  • Malassezia furfur: A fat-loving yeast that is part of normal skin flora. It causes Tinea (Pityriasis) versicolor, leading to noticeable skin pigmentation changes. It can also cause folliculitis which presents similar to inflammatory skin conditions.

Laboratory Identification of Superficial Fungi:

Clinical Sampling:

  • Skin scrapes are often used in the laboratory for examination.

  • KOH Smear: A technique used to identify the presence of budding yeast cells and hyphal fragments. The distinctive appearance is often referred to as “Spaghetti and Meatballs” in histopathological contexts.

  • Culture: Superficial fungi can grow on malt or Sabouraud's agar enriched with antibiotics, and studies often employ olive oil to facilitate growth for educational purposes.

Specific Fungi Causing Skin Conditions:

  • Exophiala werneckii: Causes Tinea nigra leading to dark discoloration on the palms and soles diagnosed by skin scrapings revealing hyphae and yeast.

Piedras:

  • Black Piedra: Caused by Piedraia hortai, presenting as gritty nodules on the hair.

  • White Piedra: Caused by Trichosporon beigelli, leading to soft granules on body hair predominantly.

Cutaneous Fungi

Cutaneous fungi thrive in areas where keratin is present, and they can infect skin, hair, and nails.

  • Keratinophilic: These organisms specialize in degrading keratin, a key component of skin and hair.

  • Dermatophytes: These are the primary agents causing cutaneous mycosis often referred to as Tinea or Ringworm.

Genera of Dermatophytes:

  1. Trichophyton: Affects skin, hair, and nails and includes species with significant clinical relevance.

  2. Microsporum: Targeted mainly to skin and hair, with some important identifiers in infections.

  3. Epidermophyton: Primarily affects skin and does not invade nails.

Ecological Groups of Dermatophytes:

  • Geophilic: Fungi that reside in soil, tend to resolve infections quickly.

  • Zoophilic: Typically parasitic on animals causing acute inflammation in humans.

  • Anthropophilic: Primarily infect humans and often lead to chronic infections that are difficult to treat.

Types of Dermatophytosis (Ringworm):

  • Tinea Corporis: Presenting as ring-shaped lesions on non-hairy skin.

  • Tinea Cruris: Known as jock itch, infects moist areas of the groin.

  • Tinea Capitis: Scalp infections with the potential to cause severe itching and hair loss.

  • Tinea Barbae: Occurs in bearded areas, leading to folliculitis-like symptoms.

  • Tinea Unguium: Involves nails and leads to nail discoloration and deformity.

  • Tinea Pedis (Athlete's Foot): Causes scaling, cracking, and itching of the feet.

  • Tinea Imbricata: Characterized by concentric ring formations on the skin.

  • Tinea Manuum: Involves the skin of the hands, often associated with Tinea Pedis.

Hair Invasion Manner:

  • Ectothrix Invasion: Involves invasion of hair from the outside with observable fluorescence under ultraviolet light.

  • Endothrix Invasion: Occurs inside the hair shaft with no fluorescence, making it less detectable.

Specific Genera of Dermatophytes:

Microsporum Species:

  • M. canis: Characterized by its spindle shape and primarily infects hair and skin.

  • M. gypseum: A geophilic fungus that does not fluoresce and primarily causes skin infections.

Trichophyton Species:

  • T. rubrum: An anthropophilic species known for its distinctive tear-drop shaped microconidia.

  • T. mentagrophytes: A zoophilic species forming grape-like clusters, typically more acute in nature.

Laboratory Diagnosis of Dermatophytes:

  • KOH Smears: Utilizing potassium hydroxide to reveal hyaline, septate hyphae under a microscope.

  • Culture on Sabouraud's Agar or Mycosel: Culturing dermatophytes should occur at room temperature for a minimum of 2 weeks to identify fungal species.

  • Dermatophyte Test Medium: A specialized medium optimized for the growth of dermatophyte fungi.

  • Wood's Lamp: A UV lamp used to highlight fluorescence specific to dermatophyte species, aiding in diagnosis.

Treatment:

  • Local Antifungals: Topical treatments such as miconazole and tolnaftate are commonly prescribed.

  • Oral Antifungals: Medications like Griseofulvin and ketoconazole are effective for systemic infections and severe cutaneous conditions.

Key Concepts: Superficial and Cutaneous Fungi

Both superficial and cutaneous mycoses are prevalent communicable diseases caused by fungi such as Malassezia, dermatophytes, or Candida species. Dermatophytes are typically inhibited by normal body temperature and serum levels, causing limited invasiveness. Geophilic and zoophilic fungi tend to lead to quick recovery post-treatment, while anthropophilic infections are chronic and challenging to manage.

Subcutaneous Fungi

Subcutaneous fungi are found deeper in the body and are acquired through skin injuries or trauma. Their infections can be severe and lead to significant morbidity:

Key Genus:

  • Sporothrix schenckii: A dimorphic fungus responsible for Rose Gardener’s Disease, identifiable by their cigar-shaped bodies in tissue.

  • Madura Foot Agents: Includes organisms like Pseudallescheria boydii that can cause multilayered granulomatous lesions.

  • Chromoblastomycosis: Resulting from darkly pigmented fungi leading to cauliflower-like lesions on the skin, diagnostic features include brownish sclerotic bodies.

  • Rhinosporidium seeberi: Causes rhinosporidiosis leading to nasal polyps; diagnostic characteristics involve observing polyp formation in nasal cavities.

  • Loboa loboi: Causes keloid-like subcutaneous nodules resulting from fungal infection.

  • Subcutaneous Zygomycosis: Associated with infections from Conidiobolus coronatus and Basidiobolus haptosporus and marked by chronic, non-invasive tissue masses.

Laboratory Diagnosis of Subcutaneous Fungi:

  • Specimen Types: Biopsies, pus, and exudate are collected for accurate diagnosis of subcutaneous infections.

  • Common Treatments: Amphotericin B is one of the standard treatments, and surgical removal of deeply set lesions may be necessary.

Key Concepts: Subcutaneous Mycoses

Subcutaneous mycoses are often caused by environmental molds found in soil and plants, emphasizing an acquired risk factor through minor skin trauma or injuries. S. schenckii is known for exhibiting notable dimorphism in human hosts, and the presence of melanized sclerotic bodies is a key diagnostic indicator. Mycetoma is characterized by localized swelling and the formation of hard, granule-like structures.