Mycology - Mine

8/13/2019 Mycology - Mine

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REVIEW OFMEDICALMYCOLOGY


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Fungus: Fungus is chlorophil free, non-photosynthetic eukaryoticorganism.

Mycology: It is the branch ofmicrobiology which deals with fungus.

Mycosis: Disease caused by fungus.


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Over 100,000 fungal species identified.

Only about 200 are human or animal

pathogens.

Most human fungal infections are

nosocomial and/or occur in

immunocompromised individuals

(opportunistic infections).

Fungal diseases in plants cause over 1billion dollars/year in losses.


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Eukaryotic microorganismsCell wall: Carbohydrate 80%(chitin,chitosan, Beta-glucan, cellulose and mannan), Protein - 10% andGlycoprotein - 10%

Chittin: Special Carbohydrate composed of longchain N-acetylglucosamine

Cell membrane: Sterol: ergosterol, zymosterol,lynosterol

Cytoplasm:mitochondria, other usual organelles.Nucleus:contain nuclear membrane and nucleoli.

Capsule: Non essential, extra layer of polysaccharide outide the cell wall.


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Fungi are heterotrophic organisms, lack of

chlorophyll (plant; autotrophic)

saprophytes, parasitesand mutualists

(symbionts i.e. lichen )

Store their food as glycogen

Both sexualand asexualspore may beproduced

To synthesize lysineby the -amino adipic acid

pathway (AAA-pathway)Bacteria and plant synthesize by

diaminopimelic acid pathway (DAP-pathway)


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Classification

On the basis of morphology Yeast

Mould

Yeast like

Dimorphic

On the basis of reproduction Ascomycotina

Zygomycotina

Basidiomycotina

Deutormycotina

On the basis of disease production (Phylogenetic)

Superficial Cutaneous

Sub-cutaneous

Deep


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Fungi- Morphological Classification

Moulds

Aspergillus

A. fumigatus

Mucorales

(zygomycetes)

Mucor spp.

Rhizopusspp.Dermatophytes

Yeasts & Yeast

like

Cryptococcus

C. neoformansC. gattii

Candida

C. albicansMalassezia

M. furfurM. globosa

Dimorphic

Moulds 250C

Histoplasma capsulatumCoccidioides immitisBlastomyces dermatitidis

Sporothrix schenkii

Yeasts/other phase/forms(370C)


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Based on size and shape of fungus

Yeast

Unicellular, spherical or elliptical structure whichreproduce by asexual budding except a few thatdivides by binary fission.

Size 8-15 x 3-5 m

They grow at 35-37 0C, body temp.

eg.Cryptococcus neoformans

Morphological classification


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Colonial morphology OFYeast...


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Yeast likeYeast with budd in chain. Budd when

not separate form long chain, look like

hyphae called pseudohyphae.

Eg. Candida species


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Mould

Multicellular, filamentous, cylindrical, elongatedstructure with branching tubules called hyphae

Diameter4-20 m

They grow at 22-25 0C, Room temp.

Eg. Dermatophytes.


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Colonial morphology of Mold...


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Hyphae Without Cross Walls

Cell wall

Nuclei

Cytoplasm

Cross wall

Cell wall

Cytoplasm

Hyphae With Cross Walls

Hyphae StructureNuclei


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Dimorphic:

Fungus which grow as yeast at 37C

and as mould at 25 C (thermally

dimorphic fungi).eg.Histoplasma capsulatum

Blastomyces dermatitidis.


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Sporothrix schenckii

Environment/Routine culture media(SDA) 25-300C ---Mold form

Tissue/Enriched media (BHI)

35-370C---Yeast form


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Classification of Fungi

Four major division of fungi

base on the type of sexual spores

(ascospore, basidiospore, zygospore, oosore)

plus another group, which have no knowsexual state. Ascomycota

Basidiomycota

Zygomycota

Chytridiomycota

Deuteromycota (Imperfect fungi)


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Division: Ascomycota

Common name: Sac fungi

Sexual reproduction: ascospore

Asexual reproduction: conidia, arthospore,budding

septate hyphae

Aspergillus sp. Penicillium sp.,


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Life cycle of Ascomycetes


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Division: Basidiomycota

Common name: Club fungi, mushroom

Sexual reproduction: basidiospore

Asexual reproduction:budding septate hyphae,

clamp connection Amanita phalloides

Mushroom:

Amanita muscaria


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Division: Zygomycota

Common name: Bread molds

Sexual reproduction: Zygospore

Asexual reproduction: Sporangiospore,

sporangium

Rhizopus sp., Mucor sp., Asidia sp.


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Life cycle of Rhizopus

sto loni fer


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Division: Chytidiomycota

Common name: Water molds

Sexual reproduction: Oospore

Asexual reproduction: Zoospore,

zoosporangium, haveflagella

aseptate hyphae

Phythium insidiosum


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Deuteromycota

Common name: Imperfect fungi

have no known sexual state in life cycle

Asexual reproduction : conidia (blastic, thallic)

septate hyphae

Human pathogenic fungi: dermatophytes,

dimorphic fungi


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Clinical classification

Based on the anatomical sites involved

1.Superficial fungal agents:Infects the outer mostlayer ie Stratum corneum of the epidermis. Eg.

Superficial fungal agents Superficial mycoses

Malassezia furfur Ptyriasis versicolor

Piedraia hortae Black piedra

Trichosporon beigelii White piedra


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2.Cutaneous fungal agents:

Lesion in the dermis but manifest by whole thickness of

skin. Eg.

Cutaneous fungal agents Cutaneous mycoses

Dermatophytes Dermatophytosis / Ring worm

3.Subcutaneous fungal agents:

Infect subcutaneous tissue. Eg.

Subcutaneous fungal agents Subcutaneous mycoses

Sporothrix schenkii Sporotrichosis

Rhinisporidium seeberi Rhinisporidiosis

Mycetoma Madurella mycetomatis

f


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4.Deep fungal agents

a)Primary fungal agents:

Cause systemic infection in healthy individual. Eg.Primary fungal agents Primary mycoses

Histoplasma capsulatum Histoplasmosis

Blastomyces dermatitidis Blastomycosis

Coccidioides imitis Coccidioidomycosis

b)Opportunistic fungal agent:

Cause systemic infection in immunocompromised individual.

Eg.

Oppurtunistic fungal agents Oppurtunistic mycosesCryptococcus neoformans Cryptococcosis

Candida albicans Candidiasis

Aspergillus fumigatus Asergillosis


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Contribution of fungus:

Beneficial effects:

1.They reside in nature and are essential in breaking

down and recycling organic matter.

2.Enhance our quality of life by contributing production offood and spirit

3.Used in medicine: Antibiotics, Adrenergic alkaloids,Immunosuppressive agents (cyclosporin).

4.Eaten as Mushroom.


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Harmful effects:

1.Fungi exert their greatest economic impact.

Agricultural industry sustains huge crop losses as aresult of fungal diseases of plants every year.

2.Fungi as Parasites

Cause serious plant and animal diseases and a

few cause diseases in humans Human Diseases

Athletes footz

Candida albicansoral thrush


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Athletes footz oral thrush


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Reproduction of fungus:

1.Asexual reproduction: Producing spore or conodia

usually by budding and binary fission.

2.Sexual reproduction: 1+1 Haploid cell = Diploid cell-

MitosisMeiosis - Haploid cell.

3. Parasexual reproduction: Meiosis in one anatomical

region but budding in other site in same strain. Exchange

of gene. Give rise to new genetic form.


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Types of diseases/disorders

1.Mycotoxicosis - caused by ingested toxins

2. Allergic- Asthma, allergic bronchopulmonary

disease, IgE and or IgG mediated

3. Colonization and invasion

-Superficial and cutaneous

-Subcutaneous

-Deep seated, disseminated

-Opportunistic mycoses

-True (endemic) mycoses


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Mycotoxicoses

Fungi can generate substance with direct

toxicity for humans and animals.

Such toxins are secondary metabolites.

They are synthesized and secreted

directly in the environment.

They include a variety of mycotoxins

elaborated by Mushrooms.


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Exposure to these toxins after their

ingestion result in a disease termed asmycetismus.

The severity of the disease depends on

the amount and type of mycotoxin

ingestion.

Heating of mycotoxins has little effects

on reducing the toxicity.

Eg.


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Amatoxins and Phallotoxins: They derivedfrom poisonous mushroom Amanita which

may yield several toxins including phalloidin,phalloin and alpha bata and gamma amanitin.

The liver is the target organ for both familiesof toxins.

Amanitin prevent messenger RNA synthesisby inhibiting cellular RNA polymeraseenzyme

The treatment of mushroom poisoning islargely supportive, as specific antidots are notavailable.


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Aflatoxins: Some fungi elaborate a

variety of mutagens and carcinogens.The most potent and best

characterized example isAflatoxin.

There are eight variety of aflatoxinsproduced by certain strains of

Aspergillus flavusand other mould.

Aflatoxin is the most potent livercarcinogen in humans and also induces

many other molecular changes.


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Laboratory diagnosis of fungal infection

Principle: It is based on demonstration offungal agents by direct microscopicexamination. Isolation and identification byculture. Serological tests and nucleic acid

based techniques are also helpful. Steps:

Collection of specimen

Skin scraping

Nail cutting

Hair plucking


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Microscopic examination:

Wet preparation after partial digestion ofkeratin tissue by 10-20% koh solution.

Gram stained smear: For yeast

Giemsa stain: For Histoplasma

capsulatum. India ink preparation: For cryptococcus

neoformans.

Calcofluor stain and Methenamine silverstain is also helpful in microscopicdiagnosis of fungi in tissue.


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Culture:

Media: Sabourrauds dextrose agarmedia

Temparature: 25-37C

Time: 2-3 weeks

Serological tests:

Detection of fungal Ag or Ab by ELISA,RIA, LA.


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Nucleic acid beased technique:

DNA Probe can be used to identify fungi

growing in culture at a much earlier stage.


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