ntroduction to mycology

1. Medical Mycology
Introduction to Basics
Dr.T.V.Rao MD
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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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4. Fungus Everywhere
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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
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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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18. CLASSIFICATION
• Depending on cell morphology
1. Yeasts
2. Yeast like fungi
3. Molds
4. Dimorphic fungi
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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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39. Mycoses
• Superficial
• Cutaneous
• Subcutaneous
•Systemic
• Opportunistic
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40. Deep mycoses
Subcutaneous mycoses Systemic mycoses
1. Mycotic 1. Cryptococcoses
Mycetoma 2. Blastomycosis
2. Chromoblastomyc 3. Coccidioidomyc
oses oses
3. Sporotrichosis 4. Histoplasmoses
4. Rhinosporidiosis
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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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