13.04.09 phase i/ module vii dr ekta, microbiology 1 classification & general properties of...
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13.04.09 Phase I/ Module VII Dr Ekta, Microbiology
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Classification & General Properties of Fungi
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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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Introduction 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-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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1. Yeasts
Unicellular fungi which reproduce by budding
On culture - produce smooth, creamy colonies
e. g Cryptococcus neoformans (capsulated yeast)
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2. Yeast like fungi Grow partly as yeasts and partly as
elongated cells resembling hyphae which are called pseudohyphae. e.g. Candida albicans
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3. 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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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
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Reproduction in fungi
Sexual - formation of zygospores, 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.
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Reproduction in fungi
Micro conidia - Small, single celled
Macro conidia –
Large, single or many celled
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Systematic classification Based on sexual spore formation: 4
classes1. Zygomycetes
2. Ascomycetes reproduce sexually
3. Basidiomycetes
4. Deuteromycetes (fungi imperfectii)
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1. Zygomycetes
Lower fungi
Broad, nonseptate hyphae
Asexual spores - Sporangiospores: present within a swollen sac- like structure called Sporangium
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1. Zygomycetes
Sexual spores - Zygospore: a resting, thick walled cell in between hyphae
e.g. Rhizopus, Mucor
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2. Ascomycetes Includes both yeasts & filamentous fungi
Narrow, septate hyphae
Asexual spores are called conidia borne on conidiophore
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2. 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.
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3. 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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4. 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
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Vegetative Structures of Fungi
Arthrospores – formed by segmentation & condensation of hyphae
Chlamydospores – thick walled resting spores
e.g. C.albicans
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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
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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
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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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Deep mycoses
Subcutaneous mycoses 1. Mycotic Mycetoma
2. Chromoblastomycoses
3. Sporotrichosis
4. Rhinosporidiosis
Systemic mycoses1. Cryptococcoses
2. Blastomycosis
3. Coccidioidomycoses
4. Histoplasmoses
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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 opportunistic infections
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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
Source of food e.g. mushrooms
Fermentation - Production of alcohol, bread, cheese e.g. Sacchromyces spps
Antibiotic production e.g. Penicillin from Penicillium notatum
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Useful Properties of Fungi
Ergot from Claviceps purpurea, used to induce uterine contractions
Vaccines for Hepatitis B – Sacchromyces cerevisiae
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Learning Objectives
Describe the general characteristics of fungi Discuss the major classes of fungi and list examples Discuss the criteria upon which fungi are categorized Explain the formation of both asexual and sexual
spores for reproduction Discuss the medical & industrial importance of fungi
Learning Resources:Learning Resources: Lecture notes Textbook of Microbiology, R. Ananthanarayan Ch 65