Medical MycologyIntroduction to Basics

Dr.T.V.Rao MD

04/11/2023 Dr.T.V.Rao MD 1

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 ergosterols3. Possess true nuclei with nuclear membrane & paired

chromosomes.4. Divide asexually, sexually or by both5. Unicellular or multicellular

04/11/2023 Dr.T.V.Rao MD 2

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

04/11/2023 Dr.T.V.Rao MD 3

Fungus Everywhere

04/11/2023 Dr.T.V.Rao MD 4

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

04/11/2023 Dr.T.V.Rao MD 5

Mycology• Present as saprophytes in soil, decaying

plants ,nature.• Eukaryotes • Known before bacteria Botanists • Developing Nations changing trends USA• More serious and even fatal diseases,

04/11/2023 Dr.T.V.Rao MD 6

FUNGI (Mycology) Diverse group of heterotrophs.

– Many are ecologically important saprophytes (consume dead and decaying 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 about

100 are human or animal pathogens.– Most human fungal infections are nosocomial and/or occur in

immunocompromised individuals (opportunistic infections).

04/11/2023 Dr.T.V.Rao MD 7

Understanding the Structure of Fungi

• Yeasts and molds have different structural and reproductive characteristics– Yeast are unicellular, nucleated rounded fungi while

molds are multicellular, filamentous fungi– Yeast reproduce by a process called budding while

molds produce spores to reproduce– Some yeast are opportunistic pathogens in that they

cause disease in immuno-compromised individuals– Yeast are used in the preparation in the variety of

foods

04/11/2023 Dr.T.V.Rao MD 8

Predisposing factors• Use of

Antibiotics,• Use of

steroids,• Immunosuppressive

conditions

04/11/2023 Dr.T.V.Rao MD 9

Fungal Diseases• Mycosis- fungal infection

– < 100 cause human disease– Not highly contagious– Humans acquire from nature

• Groups based on degree on tissue involvement and mode of entry

• Cutaneous mycoses-dermatophytes– Epidermis, hair & nails– Contagious-direct or indirect contact– Secrete keratinase that degrades keratin

04/11/2023 Dr.T.V.Rao MD 10

Fungal Morphology Hyphae (threads)

making up a mycelium Yeasts

Many pathogenic fungi are dimorphic, forming hyphae at ambient temperatures but yeasts at body temperature.

04/11/2023 Dr.T.V.Rao MD 11

Structure of Fungi• Vegetative structures involved in

catabolism 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, continuous cells with many nuclei

04/11/2023 Dr.T.V.Rao MD 12

Basic structure of Fungus• Cell wall is rigid• Contains Chitin,Mannan, Polysaccharides,Cytoplasm contains Sterols.Contains True Nuclei, Paired chromosome.Divide Sexually, Asexually or by BothCan have specialized cells

04/11/2023 Dr.T.V.Rao MD 13

Characteristics of fungiA. eukaryotic, non- vascular organisms

B. reproduce by means of spores, usually wind-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 of generations

04/11/2023 Dr.T.V.Rao MD 14

Understanding the Terms in Mycology

• Simplest Unicellular, Budding yeasts,• Tubular elongations Thread like structures

called as Hyphae • Tangled mass is called as Mycelium• Molding produces filamentous fungi.• Septate Aseptate • Grown up Aerial Mycelium• Grows into media Vegetative mycelium

04/11/2023 Dr.T.V.Rao MD 15

Understanding the Structure of Fungus

• Simplest fungus :- Unicellular budding yeast

• Hypha :- Elongation of apical cell produces a tubular, thread like structure called hypha

• Mycelium :- Tangled mass of hyphae is called mycelium. Fungi producing mycelia are called molds or filamentous fungi.

• Hyphae may be septate or non-septate04/11/2023 Dr.T.V.Rao MD 16

04/11/2023 Dr.T.V.Rao MD 17

CLASSIFICATION • Depending on cell morphology

1. Yeasts2. Yeast like fungi 3. Molds 4. Dimorphic fungi

04/11/2023 Dr.T.V.Rao MD 18

Yeasts• Unicellular fungi

which reproduce by budding

• On culture - produce smooth, creamy colonies

e. g Cryptococcus neoformans (capsulated yeast)

04/11/2023 Dr.T.V.Rao MD 19

Yeast like fungi

• Grow partly as yeasts and partly as elongated cells resembling hyphae which are called pseudo hyphae. e.g. Candida albicans

04/11/2023 Dr.T.V.Rao MD 20

Molds/ Filamentous fungi• Form true mycelia &

reproduce by formation of different types of spores.

• Vegetative/ aerial hyphae

e.g. Rhizopus, Mucor

04/11/2023 Dr.T.V.Rao MD 21

4. Dimorphic fungi• Occur in 2 forms Molds (Filaments) – 25C (soil)

Yeasts – 37C (in host tissue)

Most fungi causing systemic infections are dimorphic: – Histoplasma capsulatum– Blastomyces dermatidis– Paracoccidioides brasiliensis– Coccidioides immitis– Penicillium marneffei– Sporothrix schenkii

04/11/2023 Dr.T.V.Rao MD 22

Reproduction in fungi • Sexual - formation of Zygospore, ascospores

or basidiospores

• Asexual reproduction – budding or fission

• Asexual spores are formed on or in specialized structures.

• Vary in size, shape & colour but these characteristics are constant for a particular species.

04/11/2023 Dr.T.V.Rao MD 23

Reproduction in fungi

• Micro conidia - Small, single celled

• Macro conidia – Large, single or many celled

04/11/2023 Dr.T.V.Rao MD 24

Systematic classification

• Based on sexual spore formation: 4 classes

1. Zygomycetes 2. Ascomycetes reproduce

sexually3. Basidiomycetes4. Deuteromycetes (fungi imperfectii)

04/11/2023 Dr.T.V.Rao MD 25

Zygomycetes • Lower fungi• Broad, nonseptate

hyphae• Asexual spores -

Sporangiospores: present within a swollen sac- like structure called Sporangium

04/11/2023 Dr.T.V.Rao MD 26

Zygomycetes • Sexual spores -

Zygospore: a resting, thick walled cell in between hyphae

e.g. Rhizopus, Mucor

04/11/2023 Dr.T.V.Rao MD 27

Ascomycetes• Includes both yeasts & filamentous fungi • Narrow, septate hyphae

• Asexual spores are called conidia borne on conidiophore

04/11/2023 Dr.T.V.Rao MD 28

Ascomycetes

• Sexual spores called ascospores are present within a sac like structure called Ascus.

• Several asci may be seen within a fruiting body as seen in Penicillium, Aspergillus

• Each ascus has 4 to 8 ascospores.

04/11/2023 Dr.T.V.Rao MD 29

Basidiomycetes

• Sexual fusion results in the formation of a club shaped organ called base or basidium which bear

spores called basidiospores

04/11/2023 Dr.T.V.Rao MD 30

Deuteromycetesor Fungi imperfectii

• Group of fungi whose sexual phases are not identified.

• Grow as molds as well as yeasts.• Asexual stage – conidia e.g. Candida, Cryptococcus

04/11/2023 Dr.T.V.Rao MD 31

Vegetative Structures of Fungi

• Arthrospores – formed by segmentation & condensation of hyphae

• Chlamydospores – thick walled resting spores

e.g. C.albicans

04/11/2023 Dr.T.V.Rao MD 32

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

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 diploid nucleus

– Meiosis-diploid nucleus gives rise to haploid nuclei

– Sexual spores, some + , some -,some recombinants

– Sexual spores used to classify fungi into divisions

Fungal Infections/ Mycoses

• Superficial mycoses: – 2 types: surface and cutaneous mycoses– Skin, hair & nails. – Mild but chronic disease

• Deep mycoses:– 2 types: subcutaneous & systemic mycoses– Caused by soil saprophytes– Infection is accidental– Range from a symptomatic infection to fatal disease

04/11/2023 Dr.T.V.Rao MD 35

Superficial: Surface mycoses • Live exclusively on dead surfaces of

skin and its appendages• No contact with living tissue, hence

no inflammatory response 1. Tinea versicolor 2. Tinea nigra 3. Piedra

04/11/2023 Dr.T.V.Rao MD 36

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

04/11/2023 Dr.T.V.Rao MD 37

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.04/11/2023 Dr.T.V.Rao MD 38

Mycoses • Superficial • Cutaneous• Subcutaneous •Systemic • Opportunistic

04/11/2023 Dr.T.V.Rao MD 39

Deep mycoses

Subcutaneous mycoses

1. Mycotic Mycetoma

2. Chromoblastomycoses

3. Sporotrichosis 4. Rhinosporidiosis

Systemic mycoses1. Cryptococcoses 2. Blastomycosis 3. Coccidioidomyc

oses4. Histoplasmoses

04/11/2023 Dr.T.V.Rao MD 40

Candidiasis• Caused by candida sps, forms a

bridge between superficial & deep mycoses as it can cause cutaneous as well as systemic infections

• Can also cause opportunistc infections

04/11/2023 Dr.T.V.Rao MD 41

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

04/11/2023 Dr.T.V.Rao MD 42

Useful Properties of Fungi

04/11/2023 Dr.T.V.Rao MD 43

Source of food e.g. mushrooms

Fermentation - Production of alcohol, bread, cheese e.g. Sacchromyces spps

Antibiotic production e.g. Penicillin from Penicillium notatum

Useful Properties of Fungi

04/11/2023 Dr.T.V.Rao MD 44

Ergot from Claviceps purpurea, used to induce

uterine contractions

Vaccines for Hepatitis B – Sacchromyces cerevisiae

Diagnosis/Treatment• Grown in medium that selects for fungal

growth– 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

04/11/2023 Dr.T.V.Rao MD 45

• Programme Created by Dr.T.V.Rao MD for Medical and Paramedical Students in

the Developing World• Email

• doctortvrao@gmail.com

04/11/2023 Dr.T.V.Rao MD 46