Fungi I Flashcards by Joel Glotfelty

Their biochemistry and molecular biology are resemble those of mammalian cells

Fungi

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Molecular genetic analysis has shown that many components of the cellular machinery required for protein synthesis and secretion, transcription, DNA replication, and control of cell division are functionally interchangeable in

Human and Fugnal Cells

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Fave thick rigid cell walls that contain long-chain polysaccharides and highly-glycosylated proteins

Fungi

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The impermeable cell wall limits access of drugs to the

Cytoplasm

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An important wall component

-A polymer of D-mannose, bound to proteins

Mannan

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A ‘mannose-binding protein’ in serum, resembles C1q; it binds fungal walls and activates

Complement

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Fungi obtain nutrients and energy by breaking down organic matter, meaning they are

Saprophytes

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Because of their rigid walls fungi are incapable of

Phagocytosis

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Fungi - especially their cell walls - are potent

Immunogens

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Growing [= vegetative] fungi divide by

Mitosis

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In vegetative growth fungi produce thick-walled

-specialized for dispersal and resistance to unfavorable environments

Asexual spores (conidia)

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When conidia encounter favorable nutrition, they germinate and resume growth. The mitotic mode of growth is the

Imperfect State

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Many diploid fungi also undergo meiosis. The haploid products of meiosis are not gametes but thick-walled

Sexual Spores

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Two haploid cells of different mating type can fuse to produce a diploid cell. The ability to go through meiosis and produce sexual spores is the

Perfect State

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Takes place only under strictly-defined conditions, often involving starvation, and seldom takes place in mammalian tissue

Meiosis

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So, although sexual structures determine classification of fungi, they are of little use in the

Identification of pathogens

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Easily airborne and resistant to heat, cold, and drying.

-They are widespread in the environment

Fungal Spores

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Pose a major health problem for severely immunocompromised patients

Fungal Spores

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Immune defense against fungi is provided mostly by

Phagocytes

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Neutropenic patients (for example, those who receive radiation therapy for cancer) are highly susceptible to

Fungal Infections

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A a structural analogue of cytosine

5-fluorocytosine

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Fungi convert it to 5-fluorodeoxyuridine monophosphate, an analogue of dTMP

5-fluorocytosine

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Inhibits synthesis of thymine and blocks fungal DNA synthesis

5-fluorocytosine

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Because genetic resistance regularly emerges, 5FC is used in combination with

Amphotericin

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Membrane inhibitors exploit one of the few differences between fungal and mammalian cells: Mammalian membranes contain cholesterol, while those of fungi contain the related steroid

Ergosterol

Bind to ergosterol in the membrane, increase membrane permeability and cause loss of small molecules from the cell

Polyenes

What are two polyenes that serve as membrane inhibitors?

Amphotericin and Nystatin

Used for systemic or deepseated infections

Amphotericin

Too toxic for internal use but is used topically for fungal infections

Nystatin

What are the four types of fungal membrane inhibitors?

Polyenes, Azoles, Echinocandins, and Pentamidine

Interfere with the synthesis of ergosterol -The best antifungals

Azoles

Block synthesis of cell-wall polysaccharides

Echinocandins

Used against Pneumocystis carinii, a common cause of pneumonia in AIDS patients, and recently discovered to be a fungus

Pentamidine

Pneumocystis genes which encode ribosomal RNA contain introns that splice themselves out of rRNA transcripts without participation of the normal cellular splicing apparatus. This self-splicing is inhibited by

Pentamidine

No example of a self-splicing intron is found in mammalian DNA; this accounts for pentamidine’s

Selective toxicity

What are the four major groups of fungi?

Zygomyces, Ascomyces, Basidiomyces, and Deuteromyces

Many sexual spores are produced in a large sack-like zygospore, produced at the position at which two haploid cells have fused

Zygomyces

What are two important pathogenic zygomycetes?

Rhizopus and Mucor

Single cells undergo meiosis and the resulting four haploid spores are contained in a sac [ascus], derived from the wall of the original diploid cell

Ascomyces

What are two important non-pathogenic ascomycetes?

Bread and Brewers yeast

Diploid nuclei in a club-like structure (basidium) undergo meiosis and haploid spores bud in chains from the tip of the basidium

Basidiomyces

What is an example of an important basidiomycete?

Cryptococcus and poisonous mushrooms (Amanita)

What is an important non-pathogenic basidiomycete?

Edible mushroom

No known sexual stage. However, perfect fungi undergo meiosis only under specific conditions, it is not often known whether a deuteromycete is truly incapable of meiosis or whether the appropriate conditions have simply never been found

Deuteromyces [= fungi imperfecti]

The sporangium contains haploid spores formed by meiosis created by fusion of hyphal tips of two mating types

Zygomycete

Diploid nucleus goes through meiosis to produce 4 haploid nuclei. Each divides again, then forms a spore wall around itself

Ascomytcete

Fungi are non-fastidious. They are cultured on media such as

Saboraud's medium

Contains protein hydrosylate and glucose

Saboraud's medium

For culture, a few pathogenic fungi require

Blood agar

Cannot be cultured at all except in the lungs of immunosuppressed rats

Pneumocystis

Fungal plates are usually incubated for 30 days before being reported as

Negative

Dark-pigmented colonies are called

Dematiacious

Non-pigmened colonies are called

Hyaline

The dark pigment aids

Virulence

Unlike bacteria, many fungi have diagnostic

Morphology

Identification depends heavily on morphology of

Asexual forms

Mammalian cells are destroyed but the thick walls of fungi resist alkali, so become easier to see in tissue. Easy and rapid staining technique

Drop of KOH

This fluorescent dye binds to the polysaccharide in fungal walls -Requires a fluorescence microscope

Calcofluor

Which two stains show fungi in tissue sections?

Methenamine silver and PAS stains

Molds or filamentous fungi have cells arranged in filaments called

Hyphae

The mass of hyphae forms a

Mycelium

Cell division is by transverse fission; cross-walls [septa] are present in ascomycetes and basidiomycetes but are rare or absent in

Zygomycetes

Colonies of filamentous fungi appear

Fluffy or powdery

Unicellular fungi that reproduce by budding -Formation of a new cell begins with a small bulge in the wall of an existing cell; the bulge progressively enlarges, nuclear division takes place, one of the daughter nuclei migrates into the bud, and a septum forms that separates the two cells

Yeasts

If progeny cells remain persistently attached, they are said to form

Pseudohyphae

Yeast colonies usually appear

Moist or creamy

Dimorphic fungi grow as yeasts in the rich environment of the body (or on blood agar) at

37 degrees C

Grow as hyphae on poor medium (Saboraud’s) at 30C

Dimorphic Fungi

Hyphal forms produced in laboratory culture are not easy to distinguish, but the yeast forms in tissue have distinctive

Morphology

Small and contain only a single cell

Microcanidia

Large and contain multiple cells

Macroconidia

Macroconidia form by differentiation of a length of hypha. An example of this is

Trichophyton

Form by fragmentation of hyphae at septal planes

Arthroconidia

Form by differentiation of the terminal cell of a hypha -They are large, round, and thick-walled

Chlamydospores

Arise by budding from the tip of a specialized flask-shaped cell

Phialoconidia

Phialoconidia may be produced as single cells or in chains. Two examples of this are

Aspergillus and penicillium

Produced by budding [Example: Cryptococcus.]

Blastocondia or blastospores

Form large numbers of asexual spores contained in a sac (sporangium), borne at the top of a stalk

Zygomycetes

What are the four forms of pathogenic fungal infections?

Superficial, Cutaneous, Subcutaneous, and Systemic

Mycoses involve the outermost cornified layers of skin, hair and nails, without invasion of deeper tissue

Superficial fungal infections

Mycoses involve only the skin, again without invasion of subcutaneous tissue

Cutaneous fungal infections

Mycoses are localized infections of deeper tissue, without spread to distant sites

Subcutaneous fungal infections

Mycoses start as a focal infection, often of the lung, and spread elsewhere

Systemic fungal infections

A relatively small number of fungi are primary pathogens, capable of infecting a healthy host. A much larger number are opportunists, infecting the

Immunocompromised

Produced by fungi of low virulence; little inflammation

Superficial mycoses

May develop hyper- or hypo-pigmentation

Skin infections (pityriasis)

Fungi grow not on skin but in or on hair shafts in

Piedra

Piedra is diagnosed by microscopic examination of a scraping from the infected site. Hair infections are fluorescent; can be visualized under a

UV (woods) Lamp

Fungi that cause cutaneous mycoses are called

Dermatophytes

Cutaneous infections are called -followed by a latin adjective that describes the sight infected

Tinea

What do the following affect? 1. tinea corporis 2. tinea capitis 3. tinea cruris 4. tinea pedis 5. tinea unguium 6. tinea barbae

1. Body/skin (ringworm) 2. Scalp/hair 3. Groin 4. Feet 5. Nails 6. Beard

Lesions expand, with a rim of active infection and inflammation and a central area of healing. Scrapings for diagnosis should be taken from the

Rim, not the center

What are the three important genera of dermatophytes?

Epidermophyton, Microsporum, and Trichophyton

Distinguished by the presence or absence of microconidia and appearance of macroconidia

Dermatophytes

Infections of skin and subcutaneous tissue, usually localized and not spreading

Subcutaneous mycoces

Lesions, often on the extremities, form ulcers or papules

Subcutaneous Mycoces

A subcutaneous mass of fungi surrounded by granulomatous inflammation is a -Similar lesions are produced by Actinomycetes

Mycetoma

A common cause of subcutaneous infections [sporotrichosis]

Sporothrix schenkii

S. schenkii is dimorphic. Cells in the yeast phase are long-oval or

Cigar shaped

Histoplasma capsulatum, Blastomyces dermatitidis, Coccidiodes immitis, and Paracoccidiodes braziliensis are all species that cause

Systemic mycoses