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
Chromoblastomycosis causative agents (3)
- Fonsecaea
- Phialophora
- Cladophialophora
Phaeohyphomycosis causative agents (4)
- Alternaria
- Exophiala
- Wangiella
- Cladophialophora
Mycetoma causative agents (4)
- Madurella
- Pseudoallescheria
- Exophiala
- Acremonium
Sporotrichosis causative agent
Sporothrix schenckii
Lymphocutaneous Sporotrichosis
Dimorphic fungal infection that is limited to the arms or legs. The pathogen is found in the tropics and subtropics, in Latin America, Mexico, and Africa. It is the most common subcutaneous fungal disease in warm, humid areas of US and is also known as “Rose gardener’s disease”. At risk- avid gardeners, farmers, and artists who work with natural plant materials have the highest incidence of sporotrichosis. Also transmitted by soil, thorn pricks or wood splinters
Lymphocutaneous Sporotrichosis symptoms
Painless, nodular and ulcerative lesions are found at the site of inoculation progresses to pus-filled discharge, and are localized. NO granules are produced. May enter the lymphatic system causing secondary lesions along lymphatic vessels. The lesions will therefore occur along the regional lymphatics of the forearm. The pathogen does not enter the blood. The disease can be prevented with glove use.
Sporothrix schenckii morphology
Mold grows at 30 degrees, white. yeast grows at 37 degrees. Exhibits PAS positive budding yeast-like cells.
Pseudoallescheria boydii
Perfect or sexual form of the fungus. The asexual or imperfect form is called Scedosporium apiospermum.
Clinical spectrum of fungus has changed over time from prevalently chronic mycetoma in otherwise healthy adults to systemic opportunistic infection .
Systemic infections after solid organ transplant are relatively frequent. Also, associated with near-drowning syndrome a potentially fatal brain infection after a patient has recovered from the primary effects of aspiration of polluted water
Pseudallescheria boydii microscopic morphology
“Lollipop” forms (asexual) can be confused with Blastomyces mold form. Sexual form produces cleistothecia (spherical shaped ascus).
Fonsecaea pedrosoi
Found in rotten wood and soil. Causes invasive infection in the immunocompromised, as well as sinusitis, keratitis, fatal brain abscess. It is the most common cause of chromoblastomycosis
Fonsecaea pedrosoi morphology
Slow growth, mature in 14 days. Velvety colonies, olivaceous to brown-black or gray in color, flat to raised and folded. Hyphae are septate and branched, producing four types of conidiogenesis
Saprophytic Dematiaceous Molds Causing Subcutaneous Mycoses, also considered Common Contaminants (10)
- Pseudallescheria boydii
- Fonsecaea pedrosoi
- Exophiala (Wangiella) dermatitidis
- Phialophora verrucosa
- Cladophialophora (Cladosporium)
- Curvularia
- Alternaria
- Bipolaris
- Epicoccum
- Nigrospora
Types of Fonsecaea pedrosoi (4)
- Fonsecaea type
- Rhinocladiella type
- Phialophora type
- Cladosporium type
Fonsecaea type of Fonsecaea pedrosoi
Distill end of conidiophore develop slight swollen denticles, that bear oval, single-celled conidia, no long chains
Rhinocladiella type of Fonsecaea pedrosoi
Conidiophore bear oval conidia at tip and on side of the conidiophore
Phialophora type of Fonsecaea pedrosoi
Phialides (vase-shaped) with terminal cup shaped collarettes, produce round to oval conidia what accumulate at the apex of phialide
Cladosporium type Fonsecaea pedrosoi
Conidiophore produce shield-shaped conidia that in turn produce short branching chains of oval conidia
Exophiala (Wangiella) dermatitidis
Clinical manifestations include mycetoma, localized cutaneous infections, subcutaneous cysts, endocarditis and cerebral and disseminated infections. Phaeohyphomycosis in both normal and immunosuppressed patients.
Exophiala (Wangiella) dermatitidis morphology
Grows slowly. Shiny, black yeast-like colonies predominate. Filamentous, velvety, gray colonies. Microscopic - dark hyphae, long tubular phialides lacking collarettes and annellations; phialides produce single celled conidia in clusters without collarettes
Phialophora verrucosa
A leading cause of chromoblastomycosis in tropical climate zones. Occasionally opportunistic infections are reported including endocarditis, keratitis, and osteomyelitis
Phialophora verrucosa microscopic morphology
Flask shaped phialides formed directly from hyphae. Phialides have distinct collarette (looks like “vase of flowers”)
Cladophialophora (Cladosporium)
World-wide distribution and are amongst the most common of air-borne fungi. Trauma and exposure to soil are main predisposing factors for acquiring infections. Systemic infection is extremely rare, superficial disease is the most common. Exhibits septate hyphae, conidiophores with long branching chains of brown, smooth walled oval to slightly pointed conidia. Approximately 14 days for growth – olive to black colonies
Curvularia
Found in soil, plants in tropical or subtropical areas, may cause infections in both humans and animals. Causes keratitis, allergic sinusitis, soft tissue infection, endocarditis, opportunistic infections result in disseminated disease.
Curvularia morphology
Rapid growth, grows in 5 days. Exhibits woolly colonies- white to pinkish then olive brown or black as it matures. Has septate hyphae and conidiophores, and conidia. Conidiophores are branched, bent where conidia originate = sympodial geniculate growth. Conidia/Poroconidia, multiseptate, over-enlarged swollen central cell usually gives the conidium a curved appearance. Macroconidia have 4 to 5 cells separated by transverse septa borne on twisted conidiophores. Center cells of macroconidia grow faster and are larger than those at the ends resulting in curved or “boomerang” appearance.
Alternaria
Found in plants, soil, food, and is a common indoor and outdoor air allergen associated with asthma. Causes local cutaneous infection, nasal/sinus infection in immunocompromised, similar to zygomycosis but does not commonly disseminate, hypersensitivity pneumonitis, mycotic keratitis, osteomyelitis and peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD).
Infection associated with immunosuppressed individuals
Alternaria morphology
Fungal culture - Rapid growth, mature in 5 days, dark greenish-black. Has septate hyphae, conidiophore variable length, zig-zap appearance. Conidia - large club-shaped (narrow at apex) with both transverse and longitudinal septations, can be single or in chains. Formation of short chains of large, smooth walled, multicelled, macroconidia separated by both cross and longitudinal septa (muriform). Macroconidia are shaped like drumsticks.
Bipolaris
Found in plant debris and soil. Associated with sinusitis, skin, keratitis, peritoneum, lung, aorta, and CNS infections, sinusitis, peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD), and cerebral and disseminated infections, has been reported in both normal and immunosuppressed patients.
Bipolaris morphology
Rapid growth, mature in 5 –days, brown-black mold. Key identifying characteristics:
Knobby zigzag appearance = sympodial geniculate growth. Also macroconidia – oblong, thick walled, 3 to 5 septations
Epicoccum
Widely distributed, isolated from air, soil and foodstuff, textiles. Allergy, no documented cases of infection in humans or animals.
Epicoccum morphology
Moderate growth, mature 7-days
woolly to cottony or felty colonies. Over time, they turn to yellow to orange, orange to red, brown to black by aging. Thick clusters of short conidiophores on hyphae with repeated branching. Young conidia - round to pear-shaped, nonseptate. Mature conidia – round and multiseptated, longitudinally and transversely
Nigrospora
Widely distributed in soil, decaying plants, and seeds. RARE skin or keratitis, almost always considered contaminant, role as a pathogen unlikely
Nigrospora morphology
Rapid growth, mature 4 days
woolly colonies. The colonies are white initially and then become gray with black areas and turns to black. Hyphae are septate with short conidiophores that swell and taper at point of conidia formation. Conidia are large, round, densely black, solitary and unicellular
