Fungal Biology Quiz: Ascomycota and Mycoses

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary role of the ascus in Ascomycota during sexual reproduction?

To facilitate karyogamy and meiosis (correct)

To support the growth of bacteria

To produce complex septa

To store asexual spores

Which of the following correctly describes superficial mycoses?

They cause systemic infections in healthy individuals.

They primarily affect the hair, nails, and epidermis. (correct)

They penetrate deep into the tissues.

They are solely caused by opportunistic pathogens.

Which organism is primarily responsible for causing pityriasis versicolor?

Aspergillus niger

Trichophyton rubrum

Malassezia globosa (correct)

Candida albicans

What distinguishes systemic fungi from other types of fungi?

They may cause serious progressive systemic diseases in healthy persons. Signup and view all the answers

What is the significance of Sabouraud's agar as a mycological medium?

It encourages the growth of fungi while limiting bacterial contamination. Signup and view all the answers

Which class of fungi includes dermatophytes that cause conditions like ringworm?

Ascomycota Signup and view all the answers

What type of fungal infections are categorized as subcutaneous mycoses?

Infections that spread through skin and lymphatic systems after initial invasion Signup and view all the answers

Which of the following statements about opportunistic fungi is true?

They are commonly found in the environment or as part of normal flora. Signup and view all the answers

Which among the following statements accurately reflects the classification of mycoses?

Mycoses can be categorized as superficial, cutaneous, and subcutaneous infections. Signup and view all the answers

What is a primary characteristic that differentiates superficial mycoses from cutaneous mycoses?

Superficial mycoses are confined to the outermost layer of the skin, while cutaneous mycoses extend deeper. Signup and view all the answers

Which of the following is NOT a common method for diagnosing fungal infections?

Magnetic resonance imaging (MRI) Signup and view all the answers

In treating superficial mycoses, which class of medication is typically utilized?

Topical antifungals Signup and view all the answers

What is the predominant sterol found in fungal cell membranes that differentiates them from mammalian cells?

Ergosterol Signup and view all the answers

Which of the following antifungal treatments is most likely used for cutaneous mycoses?

Ketoconazole Signup and view all the answers

Which feature is NOT characteristic of fungi in comparison to bacteria?

Fungi reproduce only asexually. Signup and view all the answers

What is a significant difference between the cell walls of fungi and bacteria?

Fungal cell walls are composed of chitin, while bacterial walls are made of peptidoglycan. Signup and view all the answers

Which of the following statements is true concerning obligate and facultative aerobes in fungi?

Obligate aerobes require oxygen for growth, while facultative aerobes can grow with or without it. Signup and view all the answers

Which of the following best describes the eukaryotic structure of fungal cells?

Fungal cells contain membrane-bound organelles. Signup and view all the answers

Which organism is primarily associated with subcutaneous phaeohyphomycosis?

Exophiala jeanselmei Signup and view all the answers

What is the primary characteristic feature of phaeohyphomycosis observed in tissue?

Darkly pigmented septate hyphae Signup and view all the answers

Which treatment is considered the drug of choice for subcutaneous phaeohyphomycosis?

Itraconazole Signup and view all the answers

What type of infection can result from Cladophialophora bantiana?

Cerebral phaeohyphomycosis Signup and view all the answers

Which of the following statements about chromoblastomycosis is true?

Infection can be prevented by wearing shoes. Signup and view all the answers

Which characteristics differentiate actinomycotic mycetoma granules from mycotic lesions?

Actinomycotic granules are composed of thin filaments. Signup and view all the answers

What is a common treatment option for rhinosporidiosis?

Surgical removal or cauterization Signup and view all the answers

Which method is NOT used for the laboratory diagnosis of fungal infections?

RNA sequencing analysis Signup and view all the answers

What factor complicates the development of antifungal medications?

The similarity between human and fungal cells Signup and view all the answers

Which of these fungi groups is responsible for producing deadly toxins?

Ascomycota Signup and view all the answers

In the context of fungal infections, which organism is indicated as the causative agent of rhinosporidiosis?

Rhinosporidium seeberi Signup and view all the answers

What is the general habitat associated with the transmission of Rhinosporidium seeberi?

Dust and water Signup and view all the answers

Which of the following antifungal agents is NOT typically used for treating fungal infections?

Dapsone Signup and view all the answers

Which microbial feature is important in distinguishing various fungal groups?

Reproductive types Signup and view all the answers

How are polyps caused by rhinosporidiosis typically characterized?

Large and friable Signup and view all the answers

What is the primary mode of entry for fungi causing subcutaneous mycoses?

Traumatic inoculation Signup and view all the answers

Which of the following is NOT a characteristic of sporotrichosis caused by Sporothrix schenckii?

Causes extensive systemic illness Signup and view all the answers

What is the treatment recommendation for sporotrichosis after the lesions clear?

Continue treatment for 1-2 weeks Signup and view all the answers

Which subcutaneous mycosis is primarily associated with involvement in lymphatics and lymph nodes?

Sporotrichosis Signup and view all the answers

What is a common environmental source of Sporothrix schenckii?

Decaying wood and vegetation Signup and view all the answers

Which statement about subcutaneous mycoses is incorrect?

They are always life-threatening. Signup and view all the answers

What type of fungus is Sporothrix schenckii classified as?

Thermally dimorphic fungus Signup and view all the answers

What characteristic lesion typically appears at the site of a thorn injury in sporotrichosis?

Local pustule or ulcer Signup and view all the answers

Which occupational group is most frequently associated with sporotrichosis?

Gardeners and manual laborers Signup and view all the answers

What is the preferred treatment option for troublesome cases of sporotrichosis?

Short courses of oral griseofulvin Signup and view all the answers

Study Notes

Cutaneous and Subcutaneous Mycoses

Mycology is the study of fungi
Approximately 80,000 fungal species have been described, but fewer than 400 are medically important.
Less than 50 species cause more than 90% of fungal infections
Fungi are beneficial in breaking down and recycling organic matter
Fungi contribute to food and beverages (cheese, bread, beer)
Fungi produce bioactive secondary metabolites like antibiotics (penicillin) and immunosuppressants (cyclosporine)
Fungi are eukaryotes, with a higher biological complexity than bacteria
Fungal cells have a nucleus, nuclear membrane, endoplasmic reticulum, mitochondria, and a secretory apparatus
Most fungi are obligate or facultative aerobes
Fungi reproduce both sexually and asexually
Some fungi are unicellular; others become multicellular via branching filaments
Fungi absorb nutrients; they lack chlorophyll
The fungal cell wall is different from bacteria and plant cells chemically
The main sterol in fungi is ergosterol, while in mammals it is cholesterol
Fungi are typically haploid, although diploid nuclei are formed during sexual reproduction
Fungal cells are typically surrounded by a rigid cell wall
The cell wall is made up of polysaccharides (mannan, glucan, and chitin) and structural proteins
Fungal infections are termed mycoses
Mycoses can be classified as superficial, cutaneous, subcutaneous, or systemic (Table 45-1)
Systemic mycoses often exhibit subcutaneous manifestations and vice versa
Most patients with opportunistic infections have compromised host defences

Fungal Structure

Fungal cells have a nucleus, nucleolus, nuclear membrane, linear chromosomes, cytoskeleton (actin microfilaments and tubulin-containing microtubules), ribosomes, and other organelles (e.g., mitochondria, endoplasmic reticulum and Golgi apparatus)
Fungal cells have a rigid cell wall (external to cytoplasm membrane).
Fungi differ from bacterial and plant cells in their sterol composition/make up.

Yeasts and Molds

Fungi grow as yeasts or molds
Mold growth is by multicellular filamentous colonies
Colonies are composed of branching cylindrical tubules called hyphae, with diameters from 2μm – 10μm
Intertwined hyphae form a mycelium
Hyphae may be divided into cells with cross-walls or septa (like compartments), appearing at regular intervals during growth
Some medically significant molds, like zygomycetes, have hyphae that are not septated
Other fungi have septate hyphae
Aseptate (coenocytic) hyphae have multinucleated cytoplasm
Fungi grow through the development of hyphae (like extensions of the cell)
These extended hyphae form an interwoven mass referred to as the mycelium.
A portion of the mycelium (vegetative mycelium) absorbs nutrients
The aerial mycelium produces spores for reproduction
Mycelium is like a root
Aerial mycelium bears reproductive structures (conidia or spores)
The hyphae are rigid to support the interwined network which is a mold

Types of Hyphae

Vegetative hyphae penetrate the medium for nutrient absorption
Aerial hyphae extend above the surface to provide support or to reproduce.
Reproductive hyphae carry spores for reproduction.
Mycelium is a collection of hyphae

Asexual Spores on Aerial Mycelia

Sporangiospores develop in a sporangium on sporangiophore
Conidia form on conidiophore, developing from the hyphae directly or on specialized structures
- Arthrospores are conidia formed when the hyphae break down into septate segments
- Chlamydospores are thick-walled spores produced within the hyphae
- Blastospores are produced by budding
- Phialospores are formed on the outside of specialized conidiophores
- Macroconidia: Larger in size compared to microconidia
- Microconidia: Smaller in size compared to macroconidia

Yeasts

Yeasts are single cells, typically spherical or egg-shaped, with diameters of 3–15 μm.
Yeasts reproduce via budding.
Some yeasts produce buds that, rather than detaching, become elongated, producing a chain of elongated cells, called pseudohyphae.

Yeast vs. Hyphae

Pseudohyphae differ from hyphae in recurring bud-like constructions and in being less rigid
Yeasts colonize mucosal surfaces and spread to other locations (especially in immuncompromised hosts)
Pseudohyphae have enhanced nutrient scavenging capabilities, and motility.
Hyphae invade host tissues and breach endothelial cell layers. They are capable of lysing macrophages and neutrophils and exhibit thigmotropism and antigenic variation.

Reproduction

Fungi reproduce sexually or asexually
Asexual reproduction produces conidia, which arise either from condiophores or directly from existing hyphae
Sexual reproduction produces ascospores

Spores

Spores are readily dispersed
Spores are resistant to harsh environments
Spores can germinate when conditions for growth are favorable
Spores can derive from asexual or sexual reproduction

Fungal Groups

Fungi are classified into four phyla: Chytridiomycota, Zygomycota, Ascomycota, and Basidiomycota.
Ascomycota includes more than 60% of known fungi and about 85% of human pathogenic fungi
Zygomycota or Basidiomycota are the remaining pathogenic fungi

Zygomycota

Sexual reproduction results in zygospores
Asexual reproduction occurs via sporangia
Vegetative hyphae are sparsely septate

Ascomycota

Sexual reproduction involves a sac (ascus) where karyogamy and meiosis occur
Asexual reproduction is via conidia
Molds have septate hyphae.

Basidiomycota

Sexual reproduction forms four basidiospores on a club-shaped basidium
Hyphae are complex and septate.

Culturing

Fungi readily grow on simple sources of nitrogen and carbohydrates.
Sabouraud's agar is used because it doesn't support bacterial growth

Fungal Medical Significance

Various fungi (yeasts, molds, and fleshy fungi) have medical, veterinary, or agricultural importance due to causing infections
Fungal infections in humans, animals and plants are called mycoses

Grouping of Medically Important Fungi

Grouping fungi by the tissues they parasitize and diseases produced
Superficial fungi: dermatophytes (e.g., ringworm, athlete's foot)
Subcutaneous fungi cause infections in the skin and extend to subcutaneous tissue (e.g., sporotrichosis, chromoblastomycosis, phaeohyphomycosis, mycetoma)
Opportunistic fungi found in the environment or normally in the flora, producing disease in compromised situations
Systemic fungi are highly virulent and cause progressive systemic diseases (e.g., histoplasmosis)

Superficial Mycoses

Superficial mycoses involve infection of the outermost body areas (hair, nails and epidermis)

Pityriasis Versicolor

A chronic superficial infection of the stratum corneum
Caused by Malassezia globosa, M restricta, or other members of the M furfur complex
Characterized by discrete, serpentine, hyper or hypopigmented maculae mainly on the back.
Treated with selenium sulfide or azoles

Tinea Nigra

A superficial, chronic, and asymptomatic infection of the stratum corneum
Caused by Hortaea (Exophiala) werneckii
Characterized by a dark-colored discoloration, often on the palms (especially in young women).
Treated with keratolytics, salicylic acid, or azole antifungals

Piedra

Nodular infections of hair shafts
Black piedra is caused by Piedraia hortai
White piedra is caused by Trichosporon species
Treated by hair removal and topical antifungals.

Cutaneous Mycoses

Cutaneous mycoses are fungal skin infections
Caused by fungi that infect only superficial keratinized tissues (skin, hair, and nails)
Dermatophytes are the most important ones of these (Microsporum, Trichophyton, Epidermophyton)

Dermatopytoses

Dermatophytoses are among the most prevalent fungal infections
The infections are not usually life-threatening but can be troublesome
Acquired by contact with contaminated soil or infected animals/humans
Geophilic, zoophilic, or anthropophilic, depending on whether the habitat is soil, animals or humans, respectively.

Epidemiology & Immunity

Dermatophytes infections begin with trauma/contact
Susceptibility may be enhanced by factors such as moisture, warmth, skin chemistry, youth, and heavy exposure
The incidence is higher in hot/humid climates and crowded living conditions
Transmission from soil/infected animal
Trichophytin is a crude antigen preparation used to detect hypersensitivity

Tinea Pedis (Athlete's Foot)

Usually occurs as a chronic infection of toe webs
Other types include vesicular, ulcerative, and moccasin
Itching between toes, small vesicles developing, thin fluid discharge, maceration and peeling, secondary bacterial infection
Peeling/cracking are the principal manifestations, accompanied by pain and pruritus
Chronic infections

Tinea Unguium (Onychomycosis)

Nail infection following prolonged tinea pedis
Manifestations: brittle, thickened, crumbly nails

Tinea Corporis, Tinea Cruris, and Tinea Manus

Dermatophytosis affects glabrous skin
Annular lesions (ringworm) with a clearing, scaly center and red advancing border.
Usually in dry or vesicular form
Fungal metabolites, enzymes, and antigens cause erythema/vesicle formation/pruritus
Lesions expand outward
Tinea cruris (jock itch), infects the groin, may spread to scrotum
Tinea manus (hand ringworm), involves fingers/hands

Tinea Capitis and Tinea Barbae

Tinea capitis (scalp ringworm), an infection of scalp/hair follicles
Infection begins with hyphal invasion of the skin and subsequent spread down the keratinized wall of hair follicle
Infection above hair root, causes dull gray circular patches with alopecia, scaling and itching.
Tinea barbae involves the bearded region

Treatment (General)

Treatment involves removal of infected and dead epithelial structures
Topical antifungal chemicals or antibiotics are used
The area should be kept dry, sources of infection avoided

Treatment (Specific)

Scalp infections: griseofulvin for 4–6 weeks, but azoles, ketoconazole, itraconazole, and terbinafine are quite effective
Tinea corporis, pedis: itraconazole, terbinafine; topical preparations (miconazole, tolnaftate, clotrimazole, for 2-4 weeks)

Subcutaneous Mycoses

Fungi reside commonly in soil/vegetation
Enter skin/subcutaneous tissue via trauma from contaminated material/material
Lesions become granulomatous and slowly expand
Extension via lymphatics; usually confined to subcutaneous tissue but can become systemic
Sporotrichosis, chromoblastomycosis, phaeohyphomycosis, mycetoma, lobomycosis, rhinosporidiosis

Sporothrix schenckii

Thermally dimorphic fungus
Grows as mold (ambient temperatures), or budding yeast at 35-37 degrees Celsius in tissue or vitro
Causative agent for sporotrichosis
Associated with vegetation/plant materials
Acquired through traumatic inoculation
Chronic granulomatous infection with secondary spread to draining lymphatics and lymph nodes

Sporotrichosis

Chronic infection of cutaneous, subcutaneous, lymphatic tissue
Commonly seen in gardeners, forest workers, and manual laborers
Causative agent is Sporothrix schenckii
Found in soil, decaying woods, thorns, infected animals

Chromoblastomycosis

Subcutaneous fungal infection caused by traumatic inoculation of certain dematiaceous fungi
Fungal agents: Phialophora verrucosa, Fonsecaea pedrosoi, Rhinocladiella aquaspersa, Fonsecaea compacta, Cladophialophora carrionii
Chronic with gradual development of granulomatous lesions

Phaeohyphomycosis

Infections characterized by darkly pigmented septate hyphae
Forms from various species of dematiaceous molds, typically exogenous
Geographic distribution: tropical countries
Can develop as solitary encapsulated cysts, sinusitis, brain abscesses,
Treated with itraconazole or flucytosine; amphotericin B and surgery for brain abscesses

Mycetoma

A chronic, granulomatous, progressive inflammatory disease of the subcutaneous tissue
Causative agents: true fungi (eumycetes) or higher bacteria (actinomycetes)
Characterized by the formation of grains that contain aggregates of causative organisms and drain through multiple sinuses

Madura Foot

A type of mycetoma, originally reported from Madurai.
Chronic infection draining through sinuses on the skin

Rhinosporidiosis

Chronic granulomatous disease characterized by the development of friable polyps (usually in the nose, mouth, eyes, rarely genitalia, or other mucous membranes)
Distribution mainly from India and Sri Lanka, although first identified in Argentina.
Causative agent: Rhinosporidium seeberi (cannot be cultured) believed to be transmitted in dust or water, with fish as the likely natural host

Treatment (Specific, Mycetoma)

Treatments for mycetoma, including surgery, antifungal therapy (amphotericin B, miconazole, ketoconazole, itraconazole, flucytosine), topical nystatin, and topical potassium iodide.

Laboratory Diagnosis

Tissue samples, aspiration fluid, pus, biopsy material, skin scrapings, and swabs are collected
KOH mounts of specimens or histopathological examination of tissue sections stained by methanamine silver stain are used
Cultivating organisms in culture and physiological/serological tests to assist with diagnosis

Summary (Main Points)

Fungi are diverse saprophytic eukaryotes with chitin cell walls
Some fungi are unicellular and others multicellular; many fungal spores are microscopic, whilst some are large.
Reproductive types are significant for fungal group identification
Medically important fungi belong to Zygomycota, Ascomycota, Basidiomycota
Members of certain groups produce deadly toxins
Important differences in fungal cells, e.g., ergosterol, are targets for antifungal medications. Similarities between human/fungal cells pose difficulty in finding ideal targets.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the fascinating world of fungi, focusing on Ascomycota, mycoses, and their roles in different environments. This quiz covers topics such as sexual reproduction in fungi, types of mycoses, and specific fungi responsible for certain infections. Perfect for students and enthusiasts of mycology!