INTRODUCTION TO MEDICAL MYCOLOGY

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INTRODUCTION TO MEDICAL MYCOLOGY
Lecture 14
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Learning Outcome

• Able to define terms use in mycology
• Can describe basic characteristic of fungi
• Able to discuss fungal reproduction
• Able to describe mycoses
• Able to discuss laboratory examination for fungal
  infection.

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Definitions

• Mycologists--scientists who study fungi
• Mycology--scientific discipline dealing with
  fungi
• Mycoses--diseases caused in animals by fungi
• Mykos mycete fungus

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• I. FUNGI
• 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).
• Fungal diseases in plants cause over 1 billion
  dollars/year in losses.

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Characteristic of fungi

• Vegetative Hypha
• Composed of cells involved in catabolism and
  growth.
• Reproductive Hypha (aerial)
• Composed of cells involved in reproduction
  (produce spores).

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General knowledge of the fungi

• Both sexual and asexual spore may be produced
• Store their food as glycogen (plant starch)
• Fungi are heterotrophic organisms, lack of
  chlorophyll (plant autotrophic)

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General knowledge of the fungi

• Yeast unicellular, 370C
• Budding Yeast may produce a pseudohypa
• Fission yeast
• Mold multicellular, hyphae, 250C
• Dimorphic fungi (thermally dimorphic fungi)
  mold phase yeast phase

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Yeasts

• Facultative Anaerobes
• Fermentation ethanol and CO2
• Non-filamentous unicellular fungi
• Spherical or oval
• Reproduction
• a) by fission, or
• b). By budding

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Yeast Reproduction

• FISSION
• even reproduction, nucleus divides forming two
  identical cells, like bacteria
• BUDDING
• uneven reproduction, parent cells nucleus
  divides and migrates to form a bud and then
  breaks away

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YEAST

• Unicellular
• Micr. Oval to round
• (Diameter 3-15 µm)
• Macr. Pasty colonies (resemble
  bacteria)

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MOULD

• Multicellular
• Micr. . Hypha(e) (dia 2-10 µm)
• . Spores / conidia.
• Macr. .Surface texture Cottony/ powdery/
  wooly/velvety/granular/glabrous
• Pigmentation obverse reverse

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General knowledge of the fungi

• Eukaryotic microorganisms
• Rigid cell walls chitin, glucans, mannans
• Plasma membranes ergosterol
• Lysine synthesis by L-? amino adipic acid (AAA)
  pathway and other organisms synthesize lysine by
  diaminopimelic acid (DAP) pathway

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Fungal Structure

• Thallus-body
• Molds fleshy fungi have these structures
• Long filaments of cells (hyphae)
• Septate hyphae (cross wall) most fungi
• Aseptate hyphae (coenocytic ) no cross wall,
  continous mass with many nuclei .
• Mycelium
• Abundance growth of aerial hyphae resulting a
  mass can be observed with unaided ayes

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Fungal Classification

• Four groups of true fungi
• Zygomycetes (common bread moldRhizopus)
• Basidiomycetes (puffballs common mushrooms)
• Ascomycetes (Dutch elm disease/rye smut)
• Deuteromycetes (fungi imperfection)

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Classification ( cont)

• First three groups is based on their method of
  sexual reproduction
• 4th group, the Deuteromycetes, have NO sexual
  reproduction

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Fungi-Taxonomic classification

• SEXUAL SPORE CLASS
• Zygospore----------Zygomycetes
• Basidiospore--------Basidiomycetes
• Ascospore----------Ascomycetes
• None/Unknown---- Deuteromycetes
• (Fungi Imperfecti)

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Zygomycetes

• Asexual phaseSporangiumbread mold (Rhizopus
  stolonifer)
• Sexual phase--- sporgangium ---shotgun fungus
  (lives on dung) it shoots its sporgangium
  explosively towards light or fly pathogen
  (Entomophthora muscae--these types of fungi have
  been used as agents for biological control of
  insects

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Basidiomycetes

• Basidiospore
• Examples boletes, puffballs,smuts, stinkhorns
  and tooth fungi

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Ascomycetes

• Asexual phase-
• Conidiospores (Penicillium and Aspergillus)
• budding yeast
• Sexual phase (morels, lichens )

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Life Cycle

• Fungal reproduce by 2 way
• Asexual
• Sexual
• Asexual
• Hyphae fragmentation
• Asexual spores
• Conidiosphore
• Arthroconidia
• Blastoconidia
• sporangiospore

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Reproduction of Fungi

• 1. Sexual reproduction --Sexual spores
• 2. Asexual reproduction--Asexual spores
• 3. Parasexual reproduction--Genetic exchange

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Life cycle

• Conidiosphore
• Spore that is not enclosed in sac

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Life cycle

• Athroconidia
• Form fragmentation of hypae into single thick
  cells.

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Life cycle

• Blastoconidia
• Buds coming from parents cells
• Chlamydoconium a variant which spore form by
  thickening and enlargement within hypae

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Life cycle

• Sporangiospore
• Spore form inside sporangium (sac) at the end of
  sporangiophore

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Asexual Spores

• Conidiospores
• Chlamydospores
• Sporangiospores
• Blastospores
• Arthrospore

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Asexual spores ( cont)

• Conidiospore
• Multiple (chains) or single spores formed at the
  end of an aerial hypha
• Not enclosed within a sac
• Aspergillus spp.
• Penicillium spp

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Aspergillus sp.
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Conidial Fungus

• reproduces by means of asexual spores called
  conidia
• Conidia vary greatly in shape, size and color
• Most of the common household molds mildews are
  conidial fungi

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Asexual spores ( cont)

• Another type of Conidiophore
• Blastospores
• A bud coming off the parent cell
• Candida albicans

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• Chlamydospore
• Formed within hypha
• Thick-walled spore
• Candida albicans

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Chlamydospores

• The chlamydospore is a method of producing a
  substantial resting spore very quickly
• Nutrient is shunted from adjacent cells into a
  preferred cell and it swells up, converts
  nutrient materials to oil droplets for efficient
  storage, then rounds off with a thick, often
  roughened outer wall for protection

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Asexual spores

• Sporangiospores
• Hundreds formed within a sac (sporangium) at the
  end of an aerial hypha
• Rhizopus spp.
• Mucor spp
• Absidia spp

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Types of asexual spores
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SEXUAL Spores

• 1. Zygospore
• 2. Ascospore
• 3. Basidiospore
• 4. Oospore

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• Sexual spores
• Have three stages
• Plasmogamy- a haploid nucleus of donor cells
• Karyogamy- the () and (-) nuclei fuse to form a
  diploid zygote
• Meiosis the diploid nucleus give rise to
  haploid nuclei (sexual spores) genetic
  recombinant

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MYCOSES

• Superficial ( skin, hair, cornea)
• Cutaneous ( Dermatophytosis )
• Subcutaneous
• True systemic (endemic)
• Opportunistic

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Zygomycosis

• Disease caused by fungi that are classifiable as
  Zygomycetes
• Mucormycosis Order Mucorales
• Entomophthoromycosis Order Entomophthorales

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Zygomycosis (cnt)

• Presents as a spectrum of diseases, depending on
  the portal of entry and the predisposing risk
  factors of the patient
• Rhinocerebral zygomycosis
• Pulmonary zygomycosis
• Gastrointestinal zygomycosis
• Cutaneous zygomycosis
• Disseminated zygomycosis

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Material from the periorbital tissue of a woman
with poorly controlled diabetes mellitus with
facial and periorbital swelling due to
zygomycosis (see right picture) is stained with
periodic acid-Schiff stain (X 560). The material
demonstrates the classic appearance of
irregularly shaped broad hyphae with right-angle
branching (arrow).
http//www.emedicine.com/med/topic2438.htm
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Laboratory to diagnosis of fungal infection

• Specimen collection and transport
• Specimen processing
• Direct examination
• Selection and inoculation of culture media
• Identification

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LABORATORY DIAGNOSIS OF MYCOSES

• Direct microscopic examination
• Culture
• Serology

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Specimen collection and transport

• must be material from the actual infection site
• must be carefully the contamination
• must be established for the best chance of
  recovery of causative microorganisms (optimal
  times)

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Specimen collection and transport ( cont)

• must be obtained to perform the culture or other
  techniques request (sufficient quantity)
• must be used to ensure optimal recovery of
  microorganisms
• obtain cultures before the treatment
• the culture container must be properly labeled

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Specimen processing

• specimen should be examined as soon as possible
• direct examination
• KOH mount
• Calcofluor white
• India ink
• culture media

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Selection and inoculation of culture media

• Culture media for recovery of fungi from clinical
  specimens. PDA, Corn Starch Agar
• The recovery rate may be somewhat enhanced by
  using a variety of isolation media,
  considerations of cost, storage, incubator space
  and technologist time.

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Initial observations in the study of fungus
isolates

• 1.Appearance of the growth
• 2. Rate of growth
• 3. Colony pigmentation
• 4. Growth on media containing antifungal agents
• 5.Dimorphic fungi

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Initial observations in the study of fungus
isolates

• 1.Appearance of the growth
• - surface and reverse surface of colony
  were observed
• - delicate or hairlike hyphae
• 2. Rate of growth
• - saprophytes 3-5 days
• - dimorphic fungi 10 days or more
• - dermatophytes 14 days or more

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Initial observations in the study of fungus
isolates

• 3. Colony pigmentation
• 4. Growth on media containing antifungal agents
• - most strains of the dimorphic fungi can
  grow
• - most strains of the rapidly growing saprobes
  are
• inhibited
• 5. Dimorphic growth
• - mold form (the environmental and infective
  form)
• ambient or room temperature (22-25 OC)
• - yeast form (invasive form)
• near body temperature (30-35 OC)

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Preparation of mounts for study

• The tease mount
• Scotch tape preparation
• The microslide culture technique
• ( slide culture )

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Terms useful in the examination of fungi

• hypha and pseudohyphae
• mycelium
• septate or aseptate (or coenocytic) hyphae
• vegetative mycelium
• aerial mycelium
• reproductive mycelium

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Exercise

• List 4 classes of fungi
• List types of asexual spores
• Diferentiate between conidiospore with
  sporangiospores