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Introduction to Medical Mycology Basics
1. Medical Mycology
Introduction to Basics
Dr.T.V.Rao MD
11/23/2012 Dr.T.V.Rao MD 1
2. 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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3. 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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5. 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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6. 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,
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7. 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). 7
11/23/2012 Dr.T.V.Rao MD
8. 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
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9. Predisposing factors
• Use of
Antibiotics,
• Use of
steroids,
• Immunosuppressive
conditions
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10. 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
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11. Fungal Morphology
Hyphae (threads) Yeasts
making up a mycelium
Many pathogenic fungi
are dimorphic, forming
hyphae at ambient
temperatures but yeasts
at body temperature.
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12. 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
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13. 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 Both
Can have specialized cells
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14. Characteristics of fungi
A. 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
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15. 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
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16. 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-septate
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19. Yeasts
• Unicellular fungi
which reproduce
by budding
• On culture -
produce
smooth, creamy
colonies
e. g Cryptococcus
neoformans
(capsulated yeast)
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20. Yeast like fungi
• Grow partly as yeasts and partly as
elongated cells resembling hyphae which
are called pseudo hyphae. e.g. Candida
albicans
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21. 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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22. 4. Dimorphic fungi
• Occur in 2 forms
Molds (Filaments) – 25 C (soil)
Yeasts – 37 C (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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23. 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.
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24. Reproduction in fungi
• Micro
conidia -
Small, single
celled
• Macro conidia
– Large, single
or many celled
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25. 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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26. Zygomycetes
• Lower fungi
• Broad, nonseptate
hyphae
• Asexual spores -
Sporangiospores:
present within a swollen
sac- like structure called
Sporangium
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27. Zygomycetes
• Sexual spores -
Zygospore: a
resting, thick
walled cell in
between hyphae
e.g.
Rhizopus, Mucor
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28. Ascomycetes
• Includes both yeasts & filamentous fungi
• Narrow, septate hyphae
• Asexual spores are called conidia borne on
conidiophore
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29. 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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30. 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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31. Deuteromycetes
or 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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32. Vegetative Structures of Fungi
• Arthrospores –
formed by
segmentation &
condensation of hyphae
• Chlamydospores –
thick walled resting
spores
e.g. C.albicans
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33. 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
34. 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
35. 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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36. 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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37. 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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38. 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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41. 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
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42. 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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43. Useful Properties of Fungi
Source of food Antibiotic production
e.g. mushrooms e.g. Penicillin from
Penicillium notatum
Fermentation - Production of
alcohol, bread, cheese
e.g. Sacchromyces spps
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44. Useful Properties of Fungi
Ergot from Claviceps Vaccines for Hepatitis B –
purpurea, used to induce Sacchromyces cerevisiae
uterine contractions
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45. 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
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46. • Programme Created by Dr.T.V.Rao MD
for Medical and Paramedical Students in
the Developing World
• Email
• doctortvrao@gmail.com
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