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7/27/2019 13.Introduction to Mycology
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INTRODUCTION TO
MEDICAL MYCOLOGY
Lecture 14
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Mycology
Myco- fungus
Logy - study
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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).
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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 1billion dollars/year in losses.
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General knowledge of the
fungi Eukaryotic microorganisms
Rigid cell walls: made from chitin, glucans,
mannans
Plasma membranes: made from ergosterol
Lysine synthesis by L- amino adipic
acid (AAA) pathway.
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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
Mold : multicellular, hyphae, 250C
Dimorphic fungi (thermally dimorphicfungi) : mold phase & yeast phase
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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 .
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Yeasts
Facultative Anaerobes
Fermentation : ethanol and CO2
Non-filamentous unicellular fungi Spherical or oval
Reproduction:
a) fission,b). 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 abud and then breaks away
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YEAST
Unicellular
Microscopy.: Oval to round
(Diameter : 3-15 m)
Macroscopy.: Pasty colonies
(resemble bacteria)
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Yeast
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MOULD
Multicellular
Micr.: . Hypha(e) (dia: 2-10 m)
. Spores / conidia.
Macr.: .Surface texture: Cottony/ powdery/
wooly/velvety/granular/glabrous
Pigmentation :obverse & reverse
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MOULD
Hypha : septate, aseptate
Mycelium: a. Vegetative
b. Aerial /fertile/
reproductive
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Classification of Hyphae
A. Existence of septa Septate
Nonseptate ( coenocytic )B. Shape and Morphology
Racquet -
Spiral -
Nodular - Rhizoid -Root-like
Pectinate -
Favic - chandelier
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Dimorphic Fungi
Capable of growing in mould oryeast form under different
environmental conditions(temperature, CO2, nutrients)
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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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Asexual Reproduction
The progeny will be identical to parent:
Spores are called Conidiospores
Blastospores,
Chlamydospores
Sporangiospores
Fragmentation of hypahe -(Arthrospores)
Fungal spores are for reproduction,do not ensure resistance to
environmental conditions
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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
Most of the common household molds & mildewsare conidial fungi
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Aspergillus sp.
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Asexual spores ( cont)
Blastospores
A bud coming off the parent cell
Candida albicans
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Chlamydospore
Formed within hyphae
Thick-walled spore
The chlamydospore is a method of producing
a substantial resting spore very quickly.
Nutrient is shunted from adjacent cells into apreferred 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 Candida albicans
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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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Spora-spora aseksual
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Sporangiospore
1.Mucor
2.Rhizopus
3.Absidia
Cunninghamella
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1.Mucor2.Rhizopus
3.Absidia
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Cunninghamella
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(1).arthrospore
(2).chlamydospor(3).phialospore
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SEXUAL Spores
1. Zygospore
2. Ascospore
3. Basidiospore
4. Oospore
F l f
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Fungi-Taxonomic classificationis based on sexual spores
SEXUAL SPORE CLASS
Zygospore----------ZygomycetesBasidiospore--------Basidiomycetes
Ascospore----------Ascomycetes
None/Unknown---- Deuteromycetes(Fungi Imperfecti)
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Ascomycetes
Asexual phase- Conidiospores (Penicillium and Aspergillus)
budding yeast
Sexual phase (morels, lichens )
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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 asagents for biological control of insects
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Basidiomycetes
Basidiospore
Examples: boletes, puffballs,smuts,
stinkhorns and tooth fungi
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MYCOSES
Superficial ( skin, hair, cornea)
Cutaneous ( Dermatophytosis ) Subcutaneous
True systemic (endemic)
Opportunistic
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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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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 causativemicroorganisms (optimal times)
S i ll i d
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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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Sampling
In superficial mycoses the scales or infected hairsmay be stored into small sterile glass Petri
dishes.
Infected nail or skin scrapings are taken from
the deeper parts with a blunt scalpel.
Specimens from the mucous membranes orfrom orifices should be collected with dry
swabs or preferably swabs soaked in
Sabourauds broth.
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For the diagnosis of bronchopulmonary
infection morning sputum should be collected ina sterile container.
For systemic mycosis, pus swab from an ulceror aspiration from unruptured abscess, orbiopsy during surgical operation are collectedby strict aseptic technique.
For urinary tract infection, mid-stream urinesamples are collected into a wide mouth sterilecontainer.
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For cerebrospinal infections, a lumbarpuncture should de performed to
collect CSF into sterile test tubes.
For Pleural and Peritoneal Effusions, a
sample is collected by needleaspiration into sterile container.
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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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Direct Examination
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S l ti d i l ti f lt
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Selection and inoculation of culture
media
Culture media for recovery of fungi from
clinical specimens usually used is PDA,
SDA orCorn Meal Agar.
The recovery rate may be somewhat
enhanced by using a variety of isolation
media, storage, incubator time and temp.
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If the specimens are contaminated e.g. sputum,
incorporate antibiotics such as chloramphenicol
(0.5 g/l) in the media used for isolation.
Cycloheximide can also be incorporated for the
isolation of dermatophytes in order to get rid of
saprophytic fungi
The pathological material is spread upon the
surface of agar slopes. The fragments of skin,
hair or nail are planted with a firm straightpointed wire. Incubate slopes at temperature up
to 30oC
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I iti l b ti
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Initial observations
in the study of fungus isolates
1.Appearance of the growth
2. Rate of growth
3. Colony pigmentationn (Recto & Verso)
4. Growth on media containing antifungal
agents
5.Dimorphic fungi
Initial obser ations
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Initial observations
in the study of fungus isolates
1.Appearance of the growth
- surface and reverse surface of colonywere observed
- delicate or hairlike hyphae2. Rate of growth
- saprophytes : 3-5 days
- dimorphic fungi : 10 days or more- dermatophytes : 14 days or more
Initial observations
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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 saprophytes areinhibited
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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Recto Verso
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Microscopic Examination:
A Needle Mount is made as soon asspore formation is sufficiently advanced atthe center of the colony.
Place a drop of lactophenol cotton blue onthe glass surface.
With a nickel-chrome needle, pick-up a bit
of the mycelium and put it directly to thedrop of stain.
Cover it with a cover-slip and examineunder the microscope.
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Histopathological Diagnosis
To establish the diagnosis of a fungus disease,
identification should be made by a combination
of mycologic and histopathologic study.
Because of size, characteristic morphology and
histochemical composition, fungi can be studied
satisfacorily in tissues.
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Although many fungi can be seen with
haematoxylin and eosin stain (H&E), some arenot stained by this method.
Special stains for fungi are of great help in
reaching the etiologic agent. These stains are
mainly:
Periodic acid-Schiff stain (PAS).
Gomori methenamine Silver stain (GMS).
Mayers mucicarmine stain. Gridley fungal stain.
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Serological Diagnosis
Serological diagnosis of mycoses usuallylacks complete specificity because some ofthe pathogenic fungi have common
antigens. Fractional separation of the active
antigenic components of a fungus has notbeen achieved with complete success.
However, serologic techniques are usefulin reaching a presumptive diagnosis.
Th th d i l d
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These methods may include:
Double Diffusion method.
Counter-immuno electrophoresis.
Latex agglutination.
Indirect Immunofluorescence.
Indirect haemagglutination. ELISA.
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Experimental Animal infection
Experimental animal inoculation is sometimesuseful for the isolation of the causative fungus
especially in deep mycoses.
White mouse - Histoplasmosis , Cryptococcosis.
Hamsterfor Blastomycosis
Albino Rabbit for Candidosis.
Guinea-pig for experimantal infections with zoophilic
Dermatophytes.
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TYPES OF FUNGAL
INFECTION
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Superficial Fungal Infections
DERMATOPHYTES.akaTinea
YEASTS
-Pityrosporum.-Candida sp.
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TINEA Infections
T.Corporis- ringworm of body
T.Cruris- groin
T.Pedis- foot
T.Unguium- nail
T.Capitis - scalp
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Yeasts
Pityrosporum & Candida.
Ordinarily commensals.
Can become pathogens underfavourable conditions.
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Candidal Intertrigo
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Pityriasis Versicolor
hypopigmented
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T.Pedis
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