6- Introduction to Mycology - Students
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Transcript 6- Introduction to Mycology - Students
General Properties of fungi
Fungi are a diverse group of saprophytic and parasitic
eukaryotic organisms
They varies in complexity and size
ranging from the single-cell microscopic yeasts to
multicellular molds
Fungi can be distinguished from other infectious
organisms by
1- They are Eukaryotes
that is, they have a membrane-enclosed nucleus, and
other membrane bounded organelles
2- Cell wall and membrane components
Fungal cell wall are composed largely of Chitin
a polymer of N-Acetylglucosamine, rather than
peptidoglycan
The fungal membrane contains ergosterol, rather than
the Cholesterol found in mammalian membranes
3- All fungi are Heterotroph, and Chemotrophic
organisms
Fungi secrete degradative enzymes ( cellulases,
proteases, nucleases) into their immediate environment
4- Fungi are Facultative anaerobic or obligatory
aerobic organisms
5-Most fungi are Acidophilic organisms
6- Fungi reproduce and spread through the
environment by Spore formation which may be sexual
or asexual
Fungi Morphology
Fungi exist into two main forms yeasts or hyphae
(Moulds)
Some fungi may occur in both the yeast and mycelial
forms
These are called dimorphic fungi
Hyphae are multicellular filamentous structures,
constituted by tubular cells with cell walls
Hyphae of Penicillium
Yeast
Yeasts are Unicellular non-branched, oval or rounded
cells
measuring 3- 15 µm in diameter
Yeast of the species
Saccharomyces
cerevisiae
Yeasts reproduce asexually by budding (Blastospore,
and Chlamydospore)
Chlamydospores of the yeast
Candida albicans
Dimorphic fungi
These fungi are changing their morphology from
mould to yeast phase, or from yeast to mould
depending on the growth conditions
1. Yeast (parasitic or pathogenic form)
This is the form usually seen in tissue, in exudates, or if
cultured in an incubator at 37ºC
2. Mycelium ( saprophytic or mold form)
The form observed in nature or when cultured at 25ºC
Fungal Diseases
Fungal diseases can be classified into the following groups
1-Hypersensitivity (allergy)
It is an allergic reaction to molds and spores ( Indoor air pollution)
2-Mycotoxicoses
Poisoning of man and animals due to accidental ingestion of food
contaminated by toxic compounds produced by fungi
Examples
A- Ergotism: caused by Claviceps purpurea; (Ergot alkaloids)
B- Aflatoxicosis: caused by Aspergillus flavus (Aflatoxins)
Ergotism
Ergotism
3-Mycetismus
Due to ingestion of Amanitins (a toxin produced by a
specific type of mushroom ; Amanita verna )
4-Infection (Mycosis)
A-Superficial (Hair, skin, nail, cornea) mycosis
B-Subcutaneous mycosis
C-True systemic (endemic) mycosis
D-Opportunistic mycosis
SUPERFICIAL MYCOSIS
The superficial mycoses are usually limited to the
outermost layers of the skin, hair, and nails, and do
not invade living tissues
Most common Types:
1- Dermatophytosis
2- Pityriasis versicolor
Dermatophytosis (Tinea or Ringworm)
It is a type of superficial skin infection of cutaneous
layer (mainly epidermis)
Causes:
Epidermophyton
Microsporum
Trichophyton
Pityriasis Versicolor
It is a superficial chronic infection of stratum corneum.
This fungal infection is caused by Malassezia furfur
Other superficial infection of skin
Tinea Nigra, Black Piedra, and White Piedra are
caused by
Exophiala werneckii, Piedraia hortae, and Trichosporon
species respectively
Tinea Nigra
Black Piedra
White Piedra
1-Tinea Nigra
Exophiala werneckii
Infection of Stratum corneum
2-Black Piedra
Piedraia hortae
Infections of scalp hair
3-White Piedra
Trichosporon beigelii
Fungal infection of facial,
axillary or genital hair
Types of superficial Mycosis
Subcutaneous Mycosis
Sporotrichosis
Caused by Sporothrix schenkii
At 25°C: Septate hyphae, rosette-like clusters of conidia at
the tips of the hyphae
At 35 C: Yeast
Systemic Mycosis
Respiratory system infection
Chronic granulomatous pneumonia
Causes
Histoplasma capsulatum (dimorphic fungi)
Coccidioides immitis (dimorphic fungi)
Opportunistic mycosis
Candidiasis
Candida albicans infection
Example:
1-Oral Candidiasis
2-Vaginal Candidiasis
Laboratory Diagnosis of Fungal Infections
(1) Specimens
According to the site of infection
Skin scales
Hairs
Nails
Respiratory secretions
Blood
(2) Direct Detection
A- Direct microscopy of unstained preparations
(mounting method)
Examination of unstained preparations to demonstrate
hyphae, spores or yeast cells
Skin scraping, nails or hairs are mounted with 10-20% KOH
to digest the keratin layer so that hyphae and spores can be
seen
B- Direct microscopy of stained preparations
Different stains are used
India ink
Periodic acid-Schiff stain (PAS)
Silver stain
Lactophenol cotton blue stain (specific fungal stain)
(3) Culture
Sabouraud`s dextrose agar (SDA)
The standard media for most fungi
Chloramphenicol added to inhibit bacterial growth &
Cycloheximide added to inhibit saprophytic fungi
Incubation temperature is 22°C
If systemic mycosis is suspected, Enriched media is
used and incubated at 37°C
(4) Serodiagnosis
Detection of specific antibody help in diagnosis of
systemic mycosis
(5) Cutaneous delayed type hypersensitivity test
Example
Histoplasmin skin test
Histoplasma capsulatum
Blastomycin skin test
Blastomyces dermatitidis
For identification of systemic mycosis
Dermatophyte morphology