Medical Mycology Basics

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Medical MycologyIntroduction to Basics

Dr.T.V.Rao MD

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Introduction

Mykes(Greek word) : Mushroom Fungi are eukaryotic protista; differ from

bacteria and other prokaryotes.

1. Cell walls containing chitin (rigidity & support), mannan &other polysaccharides

2. Cytoplasmic membrane contains ergosterols

3. Possess true nuclei with nuclear membrane & paired

chromosomes.4. Divide asexually, sexually or by both

5. Unicellular or multicellular

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Characteristics of Fungus

Diverse group of chemo heterotrophs

> 90,000 known species

Saprophytes

Digest dead organic matter

Parasites

Obtain nutrients from tissues of organisms

Molds & mushrooms are multicellular Yeasts are unicellular

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Fungus Everywhere

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How the fungus are nourished

All are chemo heterotrophs

Absorption of nutrients: powerful

Exoenzyme Grow at lower pH-5 than bacteria

Grow in high salt and sugar

Metabolize complex CH2O like lignin in

wood-wood rot

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FUNGI (Mycology)

Diverse group of heterotrophs.

Many are ecologically important saprophytes (consume dead anddecaying matter)

Others are parasites.

Most are multicellular, but yeasts are unicellular.

Most are aerobes or facultative anaerobes.

Cell walls are made up of chitin (polysaccharide).

Over 100,000 fungal species identified. Only abou

100 are human or animal pathogens.

Most human fungal infections are nosocomial and/or occur in

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Understanding the Structure of

Fungi Yeasts and molds have different structural and

reproductive characteristics

Yeast are unicellular, nucleated rounded fungi whilemolds are multicellular, filamentous fungi

Yeast reproduce by a process called budding whilemolds produce spores to reproduce

Some yeast are opportunistic pathogens in that theycause disease in immuno-compromised individuals

Yeast are used in the preparation in the variety offoods

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Predisposing factors

Use ofAntibiotics,

Use ofsteroids,

Immunosuppressive

conditions

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Fungal Diseases

Mycosis- fungal infection < 100 cause human disease

Not highly contagious

Humans acquire from nature

Groups based on degree on tissueinvolvement and mode of entry

Cutaneous mycoses-dermatophytes Epidermis, hair & nails

Contagious-direct or indirect contact

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Fungal MorphologyHyphae (threads)

making up a myceliumYeasts

Many pathogenic fungi

are dimorphic, forminghyphae at ambient

temperatures but yeasts

at body temperature.

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Structure of Fungi

Vegetative structures involved incatabolism and growth

Thallus- in molds and fleshy fungi

Tubular filaments of cells-hyphae Septate hyphae - cross walls that divide them

into unicellular units

Pores to allow cytoplasm & nuclei to pass

Coenocytic hyphae- no septa, continuouscells with many nuclei

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Characteristics of fungiA. eukaryotic, non- vascular organismsB. reproduce by means of spores, usuallywind-disseminated

C. both sexual (meiotic) and asexual(mitotic) spores may be produced,depending on the species and conditions

D. typically not motile, although a few (e.g.Chytrids) have a motile phase.

E. like plants, fungi have an alternation ofgenerations

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Understanding the Terms in Mycology

Simplest Unicellular, Budding yeasts,

Tubular elongations Thread like structurescalled as Hyphae

Tangled mass is called as Mycelium

Molding produces filamentous fungi.

Septate Aseptate

Grown up Aerial Mycelium

Grows into media Vegetative mycelium

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Understanding the Structure ofFungus

Simplest fungus :- Unicellular buddingyeast

Hypha :- Elongation of apical cellproduces a tubular, thread like structurecalled hypha

Mycelium:- Tangled mass of hyphae is called

mycelium. Fungi producing mycelia arecalled molds or filamentous fungi.

Hyphae may be septate or non-septate

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CLASSIFICATION

Depending on cell morphology

1. Yeasts

2. Yeast like fungi

3. Molds

4. Dimorphic fungi

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Molds/ Filamentous fungi

Form true mycelia &

reproduce by formation

of different types of

spores.

Vegetative/ aerial

hyphae

e.g. Rhizopus, Mucor

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Systematic classification

Based on sexual spore formation:

4 classes

1. Zygomycetes

2. Ascomycetes reproduce

sexually

3. Basidiomycetes

4. Deuteromycetes (fungi imperfectii)

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Zygomycetes

Lower fungi

Broad, nonseptatehyphae

Asexual spores -Sporangiospores:present within a swollensac- like structure called

Sporangium

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Ascomycetes

Sexual spores calledascospores are presentwithin a sac like

structure called Ascus. Several asci may be

seen within a fruitingbody as seen inPenicillium, Aspergillus

Each ascus has 4 to 8ascospores.

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Basidiomycetes

Sexual fusion results in the formation of a club

shaped organ called base or basidium which bear

spores called basidiospores

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Deuteromycetes

or Fungi imperfectii Group of fungi whose sexual

phases are not identified. Grow as molds as well as yeasts.

Asexual stage

conidiae.g. Candida, Cryptococcus

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Asexual Spores Produced by aerial hyphae: adapted for dispersal

Progeny genetically identical to parent

Several types

Conidiospores- not enclosed in a sac produced in a chain at end of a conidiophore

Several types

Sporangiospores Within a sac, sporangium

End of sporangiophore


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Sexual Spores

Three phases of development

Plasmogamy-haploid nucleus of a donor cell (+)penetrates the cytoplasm of a recipient cell (-)

Karyogamy- the 2 nuclei fuse to form a diploidnucleus

Meiosis-diploid nucleus gives rise to haploidnuclei

Sexual spores, some + , some -,somerecombinants

Sexual spores used to classify fungi into divisions


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Superficial: Cutaneous mycoses

Cornified layer of skin & its appendages

Contact with living tissue, hence

inflammatory & allergic responses seen

1. Dermatophytes skin, hair & nails

2. 3 genera - Trichophyton

Microsporum

Epidermophyton

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CHARACTERISTICS OF FUNGI (Continued)

Dimorphic Fungi

Can exist as both multicellular fungi (molds) and yeasts.

Many pathogenic species.

Mold form produces aerial and vegetative hyphae.

Yeast form reproduces by budding.

Dimorphism in pathogenic fungi typically depends on

temperature:

At 37oC: Yeast form.

At 25oC: Mold form.

Dimorphism in nonpathogenic fungi may depend on other

factors: Carbon dioxide concentration.

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Mycoses

Superficial

Cutaneous

Subcutaneous

Systemic Opportunistic

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Opportunistic infections

Pts with debilitating disease, altered physiological

state

Mainly caused by fungi which are common lab

contaminant on culture media

Aspergillus

Pencillium

Mucor

Rhizopus

Produce serious & fatal infections

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Useful Properties of Fungi

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Source of foode.g. mushrooms

Fermentation - Production of

alcohol, bread, cheese

e.g. Sacchromycesspps

Antibioticproduction

e.g. Penicillin from

Penicillium notatum


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Diagnosis/Treatment

Grown in medium that selects for fungalgrowth

Grow at 25 C and 37 C

KOH preparations of skin biopsies Dissolves keratin in skin scrapings or biopsies

Leaves only fungal cells

Therapy- amphotericin B or ketoconazole Toxic to humans

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Programme Created by Dr.T.V.Rao MD

for Medical and Paramedical Students inthe Developing World

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Medical Mycology Basics