General Properties of Fungi
Sevtap Arikan, MD
FUNGUS• Widely distributed in nature (air,
water, soil, decaying organic debris)• ~400,000 types• Eukaryotic, highly developed cellular
structure• Facultatively anaerobic/strict aerobic• Chemotropic, nutrition: by
absorption• Nonphotosynthetic
Terminology
• Mykos: Fungus
•Mycoses: A disease caused by a fungus
• Mycology: Study of fungi
Major Developments in Mycology
• Increase in number of immunocompromised patients
• Newly developed antifungal drugs
• Antifungal susceptibility testing• Resistance to antifungal drugs
Fungi- Morphological Classification
• Yeast
• Mould
• Dimorphic
YEAST• Unicellular• Micr.: Oval to round (Dia: 3-15 µm)
Reproduce by budding Bud=Blastospore
Pseudohyphae • Macr.: Pasty colonies
(resemble bacteria)
MOULD
•MulticellularMicr.: Hypha(e) (dia: 2-10 µm)
SporesMacr.: Surface texture: Cottony/
wooly/ velvety/ granular...Pigmentation: observed
from the reverse
Mould-Definitions
•Hypha
•Mycelium: a. Vegetative b. Aerial
Classification of Hyphae
BASED ON:A. Existence of septa
Septate NonseptateB. Shape and Morphology Racquet Spiral
Nodular Root-like (rhizoid)
Pectinate Chandler
DIMORPHIC•Capable of growing in mould
or yeast form under different environmental conditions (temperature, CO2, nutrients)
•Thermal dimorphism (a group of pathogenic fungi)
Subcellular Structure of Fungi
• Capsule (present only in some fungi)• Cell wall• Cell membrane• Cytoplasm
Nucleus, nuclear membrane, nucleolus, ER, mitochondria,
vacuoles
CAPSULEStructure: Polysaccharide Functions: -Antiphagocytic
-Virulence factor
•Exist only in some fungiCryptococcus neoformans (encapsulated yeast)
CELL WALL• Antigenic in natureStructure: Multilayered
a. polysaccharides (~90%): hexose and hexosamine polymers b. proteins and glycoproteins (~10%)
Functions: Provides shape, rigidity, strength and protection from osmotic shock
Major polysaccharides of fungal cell wall
POLYMER MONOMERChitin N-acetyl glucosamineChitosan D-GlucosamineCellulose D-Glucose-Glucan D-Glucose-Glucan D-GlucoseMannan D-Mannose
• The type and amount of the polysaccharide vary from one fungal species to other.
CELLULAR MEMBRANEStructure: BilayeredPhospholipidsSterols (ergosterol, zymosterol)
Functions: a. Protects cytoplasmb. regulates the intake and secretion of
solutesc. facilitates capsule and cell wall
synthesis
FUNGAL SPORES
• Spores function in reproduction of fungi.
1. Sexual reproduction --Sexual spores
2. Asexual reproduction--Asexual spores
3. Parasexual reproduction--Genetic exchange
SEXUAL SPORES
1. Zygospore
2. Ascospore
3. Basidiospore
4. Oospore
ASEXUAL SPORES
1. Arthrospore2. Blastospore3. Chlamydospore4. Macroconidium5. Microconidium6. Sporangiospore
Fungi-Taxonomic classification
• Depends primarily on the type of sexual spore
Phylum -mycotaClass -mycetesOrder -alesFamily -ceaeGenusSpecies
Fungi-Taxonomic classification
SEXUAL SPORE CLASSZygospore----------ZygomycetesBasidiospore--------BasidiomycetesAscospore----------AscomycetesNone/Unknown---- Deuteromycetes
(“Fungi Imperfecti”)
MYCOSES
•Superficial (Hair, skin, nail, cornea)
•Subcutaneous•True systemic (endemic)•Opportunistic
LABORATORY DIAGNOSIS OF
MYCOSES• Direct microscopic examination
Gram, potassium hydroxide (KOH), calcofluor white, India ink
• Culture Sabouraud dextrose agar Mycobiotic agar
• Serology
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