Fungi Morphological Features

Questions and Answers

What is the primary method of reproduction in yeast?

Budding (correct)

Hyphal extension

Binary fission

Spore formation

What is the characteristic of yeast cells?

They are elongated and tubular

They are spherical to egg shaped (correct)

They are smaller than bacteria

They are always septate

What is the temperature at which moulds grow?

30°C

37°C

40°C

25°C (correct)

What is the characteristic of mould colonies?

They are fluffy, cottony, or powdery Signup and view all the answers

What is the function of aerial hyphae?

Reproduction Signup and view all the answers

What is unique about hyphae?

They grow at their tips by apical extension Signup and view all the answers

What is the characteristic of fungal spores?

They are resistant to heat, cold, acids, bases and other chemicals Signup and view all the answers

What is a characteristic of dimorphic fungi?

They exist as yeasts or spherules in tissues and exudates at 35-37°C Signup and view all the answers

What is the primary route of exposure to fungal spores that can trigger hypersensitivity reactions?

Inhalation of spores in the air Signup and view all the answers

What is the name of the fungal toxin produced by Aspergillus flavus?

Aflatoxin Signup and view all the answers

What is the term for fungal infections that affect the outermost layers of the skin and hair?

Superficial mycosis Signup and view all the answers

What is the type of fungal infection caused by Trichosporon beigelii?

White piedra Signup and view all the answers

What is the characteristic feature of culture in White piedra?

A cream-colored yeast-like colony with radial furrows and irregular folds Signup and view all the answers

What is the treatment for White piedra?

Removal of affected hairs and application of topical antifungal Signup and view all the answers

What is the term for fungal infections that occur in individuals with lowered immunity?

Opportunistic mycosis Signup and view all the answers

What is the name of the fungus that causes Black piedra?

Piedraia hortae Signup and view all the answers

What is the characteristic appearance of the colonies in a culture of Tinea nigra palmaris?

Black yeast colonies that may later develop to short olive-gray mycelium Signup and view all the answers

What is the primary difference between Tinea nigra palmaris and dermatophytosis?

The brown color of Tinea nigra palmaris excludes the diagnosis of dermatophytosis Signup and view all the answers

What is the recommended treatment for Tinea nigra palmaris?

Daily application of Whitfield’s ointment or 3% sulphur or 1% salicylic acid or any azole drug Signup and view all the answers

What is the characteristic appearance of the lesions in Tinea versicolor?

Superficial white, brown or fawn-colored lesions with thin scales Signup and view all the answers

What is the characteristic microscopy of Tinea nigra palmaris?

Brown, pigmented budding yeast cells with branched septate hyphae Signup and view all the answers

What is the primary reason patients seek medical care for this infection?

Due to cosmetic reasons Signup and view all the answers

What is the cause of Tinea nigra palmaris?

Exophiala werneckii Signup and view all the answers

What is the characteristic appearance of the infection in Tinea versicolor?

Discrete, serpentine, hyperpigmented or depigmented maculae Signup and view all the answers

What is the diagnostic tool used to observe the fungal hyphae in skin scrapings?

KOH digested skin scrapping Signup and view all the answers

What is the purpose of using Wood's lamp?

To observe a golden yellow fluorescence that extends beyond the periphery of the lesions Signup and view all the answers

What is the primary site of infection for Tinea nigra palmaris?

Palm of hands and fingers Signup and view all the answers

What is the recommended treatment for the infection?

Apply 2% selenium sulphide daily for 15 minutes Signup and view all the answers

What is the characteristic of Dermatophytes?

They are a group of 40 related fungi that belong to three genera Signup and view all the answers

What is the habitat of geophilic Dermatophytes?

Soil Signup and view all the answers

What is the characteristic of anthropophilic Dermatophytes?

They are usually associated with humans only Signup and view all the answers

What is the outcome of Dermatophyte infections?

Mild and chronic Signup and view all the answers

What is the primary mode of transmission of geophilic dermatophytes to humans?

By direct exposure to contaminated soil Signup and view all the answers

Which of the following is a characteristic of zoophilic dermatophyte infections in humans?

Acute and inflammatory Signup and view all the answers

What is the most common geophilic species causing human infections?

Microsporum gypseum Signup and view all the answers

What is the characteristic appearance of dermatophyte infections?

Annular scaling patch with a raised margin and less inflamed center Signup and view all the answers

What is the common name for Tinea corporis?

Ringworm Signup and view all the answers

Which of the following is a complication of interdigital fungal infection?

Bacterial cellulitis Signup and view all the answers

What is the typical age group affected by Tinea pedis?

Children and young adults Signup and view all the answers

What is the significance of knowing the species of dermatophytes and source of infection?

For proper treatment of the patient and control of the source Signup and view all the answers

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.