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