Dematiaceous molds and subcutaneous mycoses Flashcards
Dematiaceous fungi
Septate, dark-colored hyphae. The colony reverse is dark green to black. Produces melanin pigment which results in the brown, black coloring. Has hyaline hyphae that are clear and transparent (no pigment production). Includes- Alternaria , Cladosporium, Aureobasidium, Curvularia, as well as Epicoccum, Nigrospora, Bipolaris
Dermatophyte
Infections the skin, phyte= pathological growth or plant with a specific habitat
Keratinophilic
Uses keratin as a nitrogen source. Describes the causative agents of ringworm (tinea)
Dematiaceous Mold characteristics
They are ubiquitous, slow growing saprobes of soil, decaying matter, and plant pathogens. Occur worldwide and is associated with hand and foot infections in tropical environments and allergic sinusitis in the southern US. Increased cases are recorded in hospitals specializing in solid-organ transplants. Infection is documented by histopathology of hyphal invasion in sterile tissues. Melanin virulence factor, resistance to neutrophil ROS
Chitin is a possible virulence factor as chitin mutants less able to cause host infection.
How are Dematiaceous Mold infections acquired?
Humans acquire infection by entry of fungus via inhalation and trauma to skin or other body site. Involves the Dermis, Subcutaneous Tissue, Muscle, Fascia, or Bone. Low Degree Of Infectivity, humans are accidental hosts
Risk factors of fungal infections (4)
- Neutropenia
- Solid-organ transplant, bone-marrow transplant highest risk
- Chronic corticosteroid use
- Skin or soft tissue trauma
Lymphocutaneous sporotrichosis/Sporotrichosis
A chronic infection limited to cutaneous and subcutaneous tissue that may spread along lymphatics and may cause erythema, ulcerations and nodule formation
Phaeohyphomycosis
Condition of fungi with dark hyphae. Characteristics-superficial skin, keratitis, cyst formation, allergic sinusitis, disseminated infection.
>100 fungal isolates to date have been identified causing human infection. There is an absence of granule/grains (chronic deep tissue - eumycetoma) and an absence of sclerotic bodies (skin & soft tissue) chromoblastomycosis
Characteristics of dematiaceous molds causing subcutaneous mycoses
They are common soil saprobes, and infection requires traumatic introduction to deep tissue. Disease is rare. Lesions remain localized just below the skin, and infection rarely becomes systemic
Mycetoma
A chronic infection involving tumefaction, draining sinuses and granules involving cutaneous and subcutaneous tissue, fascia and bone, abscess formation. It is more prevalent in tropical and subtropical regions, such as India, Sudan, Senegal, Somalia, Venezuela, Mexico, Yemen, and the Congo. There is a 5:1 male to female ratio for infection and it is associated with farmers
Mycetoma presentation
Patients exhibit small, hard, painless lesions that eventually soften on the surface and ulcerate. They become bored out, punched in lesions with draining sinuses. Discharge is viscous, purulent fluid containing granules (red, yellow or black granules). The granules contain spores and hyphae. 66% of patients develop a secondary bacterial infection. Symptoms can last anywhere from 1 month to 25 years. Patients with diabetes are at risk for infection
Sulfur granules
The granules released in mycetoma are called sulfur granules due to their yellow color
Causative agents of mycetoma (2)
- Pseudoallescheria (Scedosporium)
- Exophiala, Acremonium, Curvularia
Chromoblastomycosis
Observed worldwide, but the majority of cases are in tropical and subtropical environments- South America or Africa. Found in soil and vegetation, inoculation usually occurs through the feet and spreads through the lymphatic system. The infection can be prevented by not going barefoot
Chromoblastomycosis symptoms
Localized, small, scaly, itchy, painless lesions. The lesions are wartlike, flat to thick, tumorous lesions described as “cauliflower-like”. They are chronic and can be nonhealing for years or decades. Inflammation, fibrosis (thickening or scaring of connective tissue), and abscess (a confined pocket of pus that collects in spaces inside the body) formation can occur in surrounding tissues.
Chromoblastomycosis diagnosis
Done through a biopsy and histological exam- the infection can invade the tissue. Patients exhibit sclerotic bodies - thick-walled, copper-colored septate cells
Chromoblastomycosis vs Phaeohyphomycosis (4 differences)
Direct microscopy of tissue is necessary to differentiate between chromoblastomycosis and phaeohyphomycosis. The key distinguishing feature between the two is the microscopic morphology of the fungal cells within tissues:
1. KOH and GMS of infected tissue
2. Golden brown sclerotic bodies
3. Distinctive from budding yeast
4. Sclerotic bodies form only in the tissue and are a unique fungal structure.
Phaeohyphomycosis morphology
NO granules, grains (R/O mycetoma) and NO sclerotic bodies (R/O chromoblastomycosis)
Where is Phaeohyphomycosis found?
Found worldwide in soil, decaying matter, plants, showers, greenhouse, pine needles. Associated with sinus infections in the Southern US and foot infections in tropical environments. Infections follow traumatic implantation
Phaeohyphomycosis symptoms
Superficial lesions to deep-seated infections such as endocarditis, sinusitis, mycotic keratitis, pulmonary and systemic abscesses, brain involvement
