Questions and Answers
What is the primary method of reproduction in yeast?
What is the characteristic of yeast cells?
What is the temperature at which moulds grow?
What is the characteristic of mould colonies?
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What is the function of aerial hyphae?
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What is unique about hyphae?
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What is the characteristic of fungal spores?
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What is a characteristic of dimorphic fungi?
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What is the primary route of exposure to fungal spores that can trigger hypersensitivity reactions?
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What is the name of the fungal toxin produced by Aspergillus flavus?
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What is the term for fungal infections that affect the outermost layers of the skin and hair?
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What is the type of fungal infection caused by Trichosporon beigelii?
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What is the characteristic feature of culture in White piedra?
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What is the treatment for White piedra?
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What is the term for fungal infections that occur in individuals with lowered immunity?
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What is the name of the fungus that causes Black piedra?
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What is the characteristic appearance of the colonies in a culture of Tinea nigra palmaris?
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What is the primary difference between Tinea nigra palmaris and dermatophytosis?
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What is the recommended treatment for Tinea nigra palmaris?
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What is the characteristic appearance of the lesions in Tinea versicolor?
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What is the characteristic microscopy of Tinea nigra palmaris?
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What is the primary reason patients seek medical care for this infection?
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What is the cause of Tinea nigra palmaris?
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What is the characteristic appearance of the infection in Tinea versicolor?
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What is the diagnostic tool used to observe the fungal hyphae in skin scrapings?
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What is the purpose of using Wood's lamp?
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What is the primary site of infection for Tinea nigra palmaris?
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What is the recommended treatment for the infection?
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What is the characteristic of Dermatophytes?
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What is the habitat of geophilic Dermatophytes?
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What is the characteristic of anthropophilic Dermatophytes?
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What is the outcome of Dermatophyte infections?
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What is the primary mode of transmission of geophilic dermatophytes to humans?
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Which of the following is a characteristic of zoophilic dermatophyte infections in humans?
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What is the most common geophilic species causing human infections?
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What is the characteristic appearance of dermatophyte infections?
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What is the common name for Tinea corporis?
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Which of the following is a complication of interdigital fungal infection?
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What is the typical age group affected by Tinea pedis?
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What is the significance of knowing the species of dermatophytes and source of infection?
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Study Notes
Morphological Features of Fungi
- Three basic morphologies of fungi: yeast, mould, and dimorphic fungi
- Yeast:
- Unicellular organism that reproduces by budding or binary fission
- Forms pseudohyphae through continued budding
- Larger than bacteria, spherical to egg-shaped
- Facultative anaerobe, prefers warmer temperatures (37°C)
- Grows rapidly (24-48 hours) and forms creamy, opaque, or pasty colonies
- Mould:
- Has branching tubular structures called hyphae
- Forms mycelia on culture media
- Colonies are fluffy, cottony, woolly, or powdery
- Grows slowly, requiring about 6 weeks
- Pattern of branching and width of mycelium aid in morphological identification
- Can be coenocytic (non-septate) or septate
- Dimorphic fungi:
- Exist as yeasts or spherules in tissues and exudates at 35-37°C
- Conversion to yeast form appears essential for pathogenicity
- Identified by morphological or biochemical characteristics and fruiting bodies
Hyphae
- May be coenocytic (aseptate and multinucleated) or septate
- Grow at their tips by apical extension
- Divided into two main types: vegetative and aerial hyphae
- Vegetative hyphae: submerged, responsible for nutrition
- Aerial hyphae: project above the surface, produce specialized structures called conidia for asexual reproduction
Fungal Reproduction
- Fungi reproduce by budding, hyphal extension, or spore formation
- Spores are resistant to heat, cold, acids, bases, and other chemicals
Fungal Spores
- Can cause tissue inflammation, necrosis, and gangrene (e.g., ergot alkaloids of Claviceps purpurea)
- Can cause liver damage and may be carcinogenic (e.g., aflatoxin of Aspergillus flavus)
- Can trigger hypersensitivity reactions, such as asthmatic attacks, rhinitis, pneumonitis, and alveolitis
Infections Secondary to Colonization
- Classified based on the part of the body affected
- Includes superficial mycosis, cutaneous mycosis, subcutaneous mycosis, systemic mycosis, and opportunistic mycosis
- Opportunistic mycosis caused by organisms of low pathogenicity that produce disease only under conditions of lowered immunity
Superficial Mycoses
- Affect the outermost layers of the skin and hair without eliciting host/pathogen hypersensitivity reactions
- Two types: Tinea (Pityriasis and Nigra) and Piedra (White and Black)
- Tinea affects the skin, while Piedra affects the hair
White Piedra
- Caused by Trichosporon beigelii
- Pathology: soft, loosely attached white or light brown nodule on axillary, pubic, beard, and moustache hairs
- Culture: cream-colored yeast-like colony with radial furrows and irregular folds
- Microscopy: septate hyaline hyphae, arthrospores, and blastospores
- Treatment: remove affected hairs and apply topical antifungal, 3% sulphur ointment
Black Piedra
- Caused by Piedraia hortae
- Pathology: firmly attached, hard, black nodule around scalp hairs
- Culture: small brown to black colonies with elevated center and flat periphery, sometimes with red pigmentation
- Microscopy: dark, thick-walled, septate hyphae with swollen irregular cells (Chlamydoconidia)
- Treatment: remove affected hairs and apply topical antifungal, 3% sulphur ointment
Tinea Nigra Palmaris
- Caused by Exophiala werneckii
- Pathology: chronic infection of stratum corneum, appearing as light brown to black non-scaly patches on palmar surface of hands and fingers
- Culture: black yeast colony that may develop into short olive-gray mycelium
- Microscopy: brown, pigmented budding yeast cells with branched septate hyphae
- Treatment: daily application of Whitfield's ointment, 3% sulphur, 1% salicylic acid, or azole drug
Tinea Versicolor (Pityriasis Versicolor)
- Caused by Malassezia furfur (Pityrosporum orbiculare)
- Pathology: chronic, non-irritating infection of stratum corneum, characterized by superficial white, brown, or fawn-colored lesions
- Culture: not usually necessary, diagnosis is mostly clinical
- Microscopy: short, unbranched hyphae or spherical cells, diagnostic with 10-20% KOH digested skin scraping
- Treatment: use of 2% selenium sulphide applied daily for a few days, or selsun shampoo
Cutaneous Mycoses
- Fungal diseases confined to outer layers of skin, nail, or hair
- Only affect keratinized layers of the body, rarely invading deeper tissues or viscera
- Fungi involved are called Dermatophytes, belonging to three genera: Microsporum, Trichophyton, and Epidermophyton
- Dermatophytes are probably restricted to non-viable skin because most are unable to grow at 37°C or in the presence of serum
- Classified as anthropophilic, geophilic, and zoophilic, depending on their usual habitat: humans, soil, or animals
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Description
Explore the three basic morphologies of fungi: yeast, mould, and dimorphic fungi, including their characteristics and growth patterns.