Principles of Mycology​-65

What rRNA types are found in mammalian mitochondria?

12S and 16S rRNA

What rRNA type is found in eukaryotic cells?

18S rRNA

What do eukaryotic cells contain that prokaryotic cells typically do not?

They contain sterol.

What structural feature is present in fungi?

Fungi have a cell wall.

What is the cellular organization of fungi?

Back:
Fungi can be unicellular or may differentiate and become multicellular by the development of branching filaments.

Are acute diseases common in fungal infections?

Acute diseases, such as those produced by many viruses and bacteria, are uncommon with fungal infections.

What are examples of primary and secondary fungal metabolites?

Primary: citric acid, ethanol, glycerol
Secondary: antibiotics (e.g. penicillin), amanitins, aflatoxins

What is the fungal lifestyle classification?

Fungal lifestyle is chemoheterotrophic.

What ecological roles can fungi occupy?

Fungi can be saprobes, symbionts, commensals, parasites

What is classic fungal taxonomy based on?

Classic fungal taxonomy is based on cellular morphology and spore production.

What is modern fungal taxonomy based on?

Modern taxonomy is based on ultrastructure, biochemical, and molecular characteristics.

What is a teleomorph in fungal classification?

Teleomorph = form that produces sexual spores.

What is an anamorph in fungal classification?

Anamorph = form that produces asexual spores.

What are examples of teleomorph and anamorph forms of the same fungus?

Ajellomyces capsulatum = teleomorph
Histoplasma capsulatum = anamorph

What are fungi called when no teleomorph is known?

Fungi imperfecti (form division Deuteromycota)

Which fungal form is more clinically relevant?

Clinically, the anamorph is more relevant.

What are key structural features of the fungal cell?

Fungi are eukaryotic organisms (with nucleus, chromosomes, organelles). They have a rigid cell wall composed of chitin and glucan, a plasma membrane with ergosterol as the major sterol, and may be unicellular or multicellular.

What stain can be used to visualize chitin in fungal cells?

Chitin can be stained with calcofluor-white.

What is the major sterol in the fungal plasma membrane?

Ergosterol is the major sterol in the plasma membrane.

What are key characteristics of yeasts?

Yeasts reproduce by budding or fission, may form pseudohyphae, are usually unicellular, and produce round, pasty or mucoid colonies.

What are key characteristics of molds?

Molds are multicellular and consist of hyphae that elongate at their tips by apical extension. They have coenocytic or septate hyphae, produce mycelium (colonies are filamentous, hairy, or woolly), and have both vegetative and aerial hyphae.

Which fungi typically have septate hyphae?

Many ascomycetes have septate hyphae.

Which fungi have coenocytic hyphae?

Mucormycetes (zygomycetes) have coenocytic hyphae.

Which fungi have septate hyphae with clamp connections?

Basidiomycetes have septate hyphae with clamp connections.

Which fungi have hyphae with arthroconidia?

Coccidioides spp. have hyphae with arthroconidia.

What is a characteristic of nonseptate hyphae?

Nonseptate hyphae contain multiple nuclei.

What is a characteristic of septate hyphae?

Septate hyphae divide nuclei into separate cells.

What type of spore formation is seen with Mucormycetes (Zygomycetes), and what structures are involved?

Asexual spore formation and associated structures are seen with Mucormycetes (Zygomycetes).

What structure contains sporangiospores?

Sporangiospores are contained within a structure called a sporangium

What type of asexual spore formation is seen with Aspergillus species (an example of a Euascomycete)?

Conidia are borne naked on a specialized structure; this is a form of asexual spore formation seen with Aspergillus species.

How do arthroconidia develop?

Arthroconidia develop within the hyphae and eventually break off.

What are chlamydoconidia and how do they develop?

Chlamydoconidia are larger than the hyphae and develop within the cell or terminally.

What are sporangioconidia and where do they form?

Sporangioconidia are borne terminally in a sporangium sac.

How do simple conidia form?

Simple conidia arise directly from a conidiophore.

What are the major fungal phyla that cause disease in humans?

Mucormycetes, Basidiomycetes, Ascomycetes, Pneumocystidomycetes, Saccharomycetes, Eurotiomycetes

What are Microsporidia, and give examples?

Microsporidia are obligate intracellular, unicellular, spore-forming eukaryotes; examples include Encephalitozoon and Nosema.

What are key characteristics of Mucormycetes (Zygomycetes)?

Mucormycetes are molds with sparsely septate, coenocytic hyphae, irregular width, and broad angle of branching. They produce sexual zygospores (by fusion of compatible mating types) and asexual sporangiospores. Root-like structures called rhizoids can be present in some genera.

What are examples of Mucormycetes?

Examples include Rhizopus and Mucor.

What are key characteristics of Basidiomycetes?

Basidiomycetes are typically filamentous, though some are yeasts. They exhibit budding yeasts, hyphae, and arthroconidia. Their hyphae have clamp connections. Sexual reproduction results in haploid basidiospores formed on a basidium.

What are examples of Basidiomycetes?

Examples include Cryptococcus and Malassezia.

[Ascomycete subgroup] What are the characteristics of Pneumocystidomycetes?

Pneumocystidomycetes have trophic forms and cyst-like structures.
Example: Pneumocystis jirovecii

[Ascomycete subgroup] What are the characteristics of Saccharomycetes?

Saccharomycetes include budding yeasts, hyphae, and pseudohyphae.
Examples: Candida, Saccharomyces

[Ascomycete subgroup] What are the characteristics of Eurotiomycetes?

Eurotiomycetes have budding yeasts, septate hyphae, and asexual conidia borne on specialized structures.
Examples: Dermatophytes, Blastomyces, Coccidioides, Histoplasma, Aspergillus

Ascomycete] What is the typical morphology of Ascomycete hyphae?

Ascomycetes have septate hyphae with fairly regular, tube-like width.

What defines fungal colonization?

Colonization is a transient or chronic association with the host, without interference with normal physiological functions.

What defines a fungal disease (mycosis)?

A fungal disease (mycosis) is a fungus-host association (infection) that results in a pathological process with harmful effects on physiological functions due to one or more of the following:
– Fungal growth
– Production of toxins
– Immunological response to the pathogen

What is a strict (primary) fungal pathogen

A strict (primary) pathogen causes disease in healthy hosts without the need for predisposing facto

What are the major types of fungal-related diseases or toxicities?

• Mycoses: Infections and allergies

• Mycotoxicoses: Poisoning with mycotoxins (e.g., neurotoxins, hepatotoxins)

• Mycetism: Mushroom poisoning

What are superficial mycoses, and give an example?

Superficial mycoses are limited to superficial surfaces of skin and hair.
Example: Pityriasis versicolor (discoloration or depigmentation and scaling of skin) caused by Malassezia furfur.

What are cutaneous mycoses, and give an example?

Cutaneous mycoses are infections of the keratinized layers of skin, hair, and nails. Symptoms include itching, scaling, broken hairs, ring-like patches on skin, and thickened, discolored nails.
Example: Dermatophytes.

What are subcutaneous mycoses, and give examples?

Subcutaneous mycoses affect deeper layers of skin, cornea, muscle, and connective tissue. They result from traumatic inoculation and cause localized infection, abscesses, ulcers, and draining sinus tracts. The immune response can lead to tissue destruction and pseudoepitheliomatous hyperplasia.
Examples: Sporothrix schenckii, Fusarium spp.

What are endemic mycoses, and what fungi cause them?

Endemic mycoses are caused by dimorphic fungi that exist in both yeast and mold forms. They are generally confined to specific geographic regions. These are systemic mycoses with primary infection in the lungs and possible dissemination to other organs/tissues. They are considered true pathogens.
Examples include:

• Histoplasma capsulatum

• Paracoccidioides brasiliensis

• Blastomyces dermatitidis

• Talaromyces (Penicillium) marneffei

• Coccidioides immitis, C. posadasii

What are opportunistic mycoses, and what fungi cause them?

Opportunistic mycoses are caused by environmental or commensal fungi with low or limited virulence (except Cryptococcus spp.). They occur primarily in debilitated or immunosuppressed individuals, and can be associated with implants or catheters.
Examples include:

• Candida spp.

• Cryptococcus spp.

• Aspergillus spp.

• Pneumocystis jirovecii

• Mucormycetes: Mucor spp., Rhizopus spp.