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Flashcards in Mycology I Deck (33):

What components of the innate immune system are largely responsible for protection against fungal infections

Professional phagocytes (neutrophils, macrophages and dendritic cells), the complement system, and PRR


Humoral immunity against fungi

- Antibodies can be detected during most fungal infections
- There is little evidence that an antibody response contributes to immunity against most fungi


Cellular immunity against fungi

- If fungal cells escape phagocytosis, then the dominant effect occurs through the interaction of dendritic cells and macrophages that results in the production of IL-12 and IFN-γ, leading CD4 cells to differentiate to Th1 cells
- Subsequently, macrophages containing multiplying fungi are activated by cytokine mediators that are produced by T-lymphocytes that have encountered fungal antigens
- Infection ultimately controlled by activated macrophages


Superficial mycoses

Malassezia furfur
Hortaea werneckii/ Exophiala Werneckii
Piedraia hortae


Cutaneous mycoses

Dermatophytes: Trichophyton, Epidermophyton and Microsporum


Subcutaneous Mycoses

Sporothrix schenckii


Opportunistic Mycosis

Pneumocystis jirovecii
Pneumocystis carinii


Malassezia furfur

Infection/disease: Pitryiasis (Tinea) versicolor
Morphology: Lipophilic yeast; hyphae produced infrequently; growth in cultures requires source of lipid
Epidemiology: Tropical and subtropical regions; not found as saprophyte in nature; passed between humans by direct or indirect transfer of infected keratinous material


Malassezia furfur
Clinical syndromes:
Laboratory Diagnosis:

Clinical syndromes: Small hypopigmented or hyperpigmented macules; affected areas don't tan
Laboratory Diagnosis: Direct microscopic visualizations in KOH preparation; calcofluor white also used to visualize; Wood lamp - lesions fluoresce a yellow color
Treatment: Spontaneous resolution not likely; localized infection treat with topical azoles or selenium sulfide shampoo


Hortaea Werneckii/ Exophiala Werneckii

Infection/Disease: Responsible for Tinea nigra
Morphology: Dematiaceous (dark colored) frequently branched hyphae
- In culture on standard mycologic medium at 25° a black mold with annelloconidia observed


Hortaea Werneckii/ Exophiala Werneckii
Clinical Syndromes:
Laboratory Diagnosis:

Epidemiology: Dark warm moist environment; Africa, Asia, and Central and South America; contracted by inoculation into superficial layers of the epidermis
Clinical Syndromes: Solitary, irregular, pigmented macule, usually on palms or soles; can resemble malignant melanoma (not contagious)
Laboratory Diagnosis: Direct microscopic visualization in KOH preparation
Treatment: Responds well to topical agents: azoles and terbinafine


Piedraia Hortae

Infection/Disease: Responsible for black piedra
Morphology: Brown to reddish black mold that exhibit asci (sexual spores) as the culture ages
Epidemiology: Uncommon, but can be found in Latin America and Central Africa (poor hygiene)


Piedraia Hortae
Clinical syndromes:
Laboratory Diagnosis

Clinical Syndromes: The presence of hard dark nodules that surround the hair shaft; asci present in cement-like substance that holds the hyphal mass together
Laboratory Diagnosis: Cultivated on routine mycological medium at 25°C
Treatment: Can be cured with a haircut, proper/regular washings and topical antifungal agents


Trichosporon: T. Inkin, T. asahii and/or T. mucoides
Clinical Syndromes:

Infection/Disease: Responsible for white Piedra
Morphology: Yeast-like fungus; hyphal elements
Epidemiology: Occurs in tropical and subtropical regions (poor hygiene)
Clinical Syndromes: Affects hair of groin and axillae; fungus surrounds hair shaft and forms white brown swelling


Trichosporon: T. Inkin, T. asahii and/or T. mucoides
Laboratory Diagnosis:

Laboratory Diagnosis: If microscopic examination reveals hyphal elements, arthroconidia and/or budding yeast, hair shaft can be cultures on mycologic media without cycloheximide (inhibits growth of Trichosporon); In culture, exhibits cream-colored, dry, wrinkled colonies
Treatment: Removal of infected hair, improved hygiene and topical azoles agents



- Very similar and closely related group of fungi that cause a wide variety of clinical disease
- Approximately 41 species of fungi recognized as dermatophytes
- All have the ability to infect superficial keratinized tissues


Tineas or ringworms (Dermatophytoses)

- Tinea capitis-scalp (Endothrix-arthroconidia inner hair shaft; Ectothrix-arthoconidia - outer hair shaft; favic)
- Tinea pedis-foot
- Tinea barbae - beard
- Tinea corporis - smooth of glabrous skin
- Tinea Cruris - groin
- Tinea unguium - nails


Dermatophytes - Morphology

The pattern of growth observed in culture along with the production/appearance of macroconidia and microconidia are distinct for each genus
- Microscopic examination of infected skin exhibit hyaline septate hyphae, chains of arthroconidia and dissociated arthrocondia
- Most unable to grow at 37° or w/ serum


Production of Macroconidia or microconidia

Epidermophyton: Macroconidia
Microsporum: Macroconidia and Microconidia (rare)
Trichophyton: Macroconidia (rare) and microconidia


Dermatophytes - Ecology (Three categories)

Zoophilic - animals
Geophilic - soil (Strong host response - highly inflamed lesions)
Anthrophilic - humans (Chronic infection with mild host response that can be difficult to cure)


Which two dermatophytes account for 80-90% of worldwide infections

Trichophyton rubrum and T. Mentagrophytes


Dermatophytes - Clinical Symptoms:

- Tinea pedis will exhibit itching vesicles and pustules, cracked skin, peeling, watery discharge
- Tinea coporis and Tinea cruris can exhibit a tiny red pimple, with itching and subsequent peripheral spreading
- Tinea capitis will spread peripherally with patches of broken hair stumps
- Tinea unguium - nails will appear thickened, cracking and have yellowish-brown color


Dermatophytes - Laboratory Diagnosis:

- Direct microscopic observation of specimens
- Some fluoresce a distinct color when exposed to a wood lamp
- Cultured on dermatophyte test media
Phenol red pH indicator included which changes from yellow to red when medium becomes alkaline from dermatophytes


Dermatophytes - Treatment

- For infections that do not involve the hair or nails, topical antifungal agents are usually effective
- For chronic skin infections involving T. rubrum - oral antifungal agents may be necessary
- For infections involving hair and nails - oral antifungal agents usually administered
- For infections of the nail - PinPoint laster therapy


Sporothrix Schenckii (Most common Fungal infection in US)

- Responsible for lymphocutaneous sporotrichosis
- Inoculation occurs through traumatic introduction through the dermis
- Found in soil and decaying matter


Sporothrix Schenckii- Morphology:

Thermally dimorphic fungus (mold at room temp; yeast at body temp)
Mold exhibits tan, brown, or black color with hyaline, septate hyphae
Yeast form spheric, oval or elongated
- Rarely seen on histological exam of tissue


Sporothrix Schenckii - Epidemiology

Usually sporadic infection and occurs in warmer climates
- Major endemic areas are Japan, NA and SA


Sporothrix Schenckii - Clinical Syndromes

Usually the primary site of inoculation is non or mildly painful and will appear as nodular lesion that will eventually ulcerate
- The infection can spread through the lymphatics that drain the site


Sporothrix Schenckii - Laboratory Diagnosis

Culturing leads to most definitive diagnosis
Incubating the plate at room temp for 2-4 days will lead to growth of mold
37° will lead to growth of yeast


Sporothrix Schenckii - Treatment

In developing countries - Potassium iodide solution
- Potassium Iodide has adverse side effects including nausea and salivary gland enlargement
- Itraconazole is safe and effective but must be administered for 3-6 mo


Pneumocystis lifecycle

Organism has never been grown in vitro
- Cystic structure that contains elliptical subunits that grow and repeat the cycle on rupture
- Three stages: trophic, precyst, and cyst
- Trophic form surrounded by a cell wall and plasma membrane containing a nucleus and several mitochondria
- The precyst subsequently matures into a cyst which contains 8 "spores"


Pneumocystis jirovecci/ Pneumocystis carinii - Epidemiology

All individuals are exposed to this organism - most seropositive by age 4
Active infections rare
Patients at risk when CD4+ T cells fall below 200 cells/mm³


Pneumocystis jirovecci/ Pneumocystis carinii - Clinical Disease:
Laboratory Diagnosis:

Clinical Disease:
- Insidious onset of pneumonia
- Presents as severe progressive interstitial pneumonia
- Frothy pulmonary edema with cellular infiltrate
- Mortality rate high among untreated patients
Laboratory Diagnosis: Microscopic identification of organism in sputum, bronchoscopy, bronchoalveolar lavage sample