Introduction to Mycology &
Laboratory Diagnosis of fungal
infections
Predisposing factors
• Pts. with debilitating diseases (TB, HIV & cancers)
• Diabetes
• Corticosteroid or antimetabolite therapy impaired immunity
• Long term intravenous cannulation
• Gastro intestinal surgical procedures
• Long term Chemotherapy
• Moist & opposing folds
• Obesity
• Pregnancy
Introduction
• Study of fungi is called Mycology
• Name is derived from Mykos meaning mushroom
• All fungi are eukaryotic – Protista
• Water, soil & decaying organic debris are natural
habitats
• Fungi are obligate or facultative aerobes
Contd…
• Fungi are chemotrophic organisms i.e obtaining
nutrients from chemicals in nature
• Some fungi are useful to man such as edible
mushrooms
• Certain yeasts are used in fermentation of juices
& some fungi in elaborating antibiotics
(Penicillium)
FUNGI BACTERIA
Eukaryotes Prokaryotes
Posses rigid cell wall containing chitin, Cell wall consists of teichoic acid
mannan and polysaccharides muramic acid and lipopolysaccharides
Cytoplasmic membranes- contain sterols Lack sterol
Cytoplasm consists of organelles such as Lack mitochondria and endoplasmic
endoplasmic reticulum and mitochondria reticulum
True nucleus with nuclear membrane and Single chromosome without nuclear
paired chromosomes are present Fungi membrane is present
may be unicellular or multicellular
Seen as yeast or moulds Seen as cocci, bacilli and spirals
Reproductive spores are formed Non-reproductive spores are formed
Most of them divide by sexual or asexual Divide by binary fission
methods
Morphological Classification
• Yeasts
• Yeast like fungi
• Moulds
• Dimorphic fungi
Yeasts
• Unicellular – Round to oval in shape
• Reproduce by budding
• Form creamy mucoid
colonies on culture media
Eg: Cryptococcus neoformans
Yeast like Fungi
• Partly as Yeasts & Partly as chains
of elongated budding cells joined
end to end forming
Pseudohyphe
Eg: Candida albicans
Moulds
• Fungi grow as branching filaments – Hyphae
• Hyphae –– septate or
non septate
• Mycelium – Tangled
mass of hyphal growth
• Dermatophytes
• Aspergillus
• Penicillium
• Rhizopus
Contd..
Dimorphic Fungi
• Exist as yeasts & mycelial forms
• Yeasts in host tissue & in cultures
at 370C
• Mycelial or hyphal forms in soil & in
cultures at 22 – 250C
Eg: Fungi causing systemic infections
– Histoplasma capsulatum
– Sporothrix schenckii
– Paracoccidioides immitis
– Blastomyces dermatitidis
Classification of fungal
diseases
• Superficial mycoses
• Subcutaneous mycoses
• Systemic mycoses – endemic systemic
mycoses
• Opportunistic mycoses
Mycoses
Surface infections involving
Skin, nail, hair & mucosa
Superficial mycoses
Eg: dermatophytosis
Pityriasis versicolor
Tinea nigra
Subcutaneous Black piedra
mycoses
progressive local disease
Systemic mycoses
tissue destruction & sinus
Formation •Blastomycosis
•Histoplasmosis
Eg: Mycetoma •Cryptococcosis etc..
Chromoblastomycosis
Sporotrichosis Deep mycoses-
Rhinosporidiosis
subcutaneous &
systemic mycoses
• Superficial mycoses.
Superficial mycoses are limited to the outermost layers of
the skin and hair- dead layers of skin- no inflammatory
response
The Cutaneous Mycoses. These are superficial fungal
infections of the skin, hair or nails. No living tissue is
invaded- cornified layers of skin-inflammatory response-
allergic reactions
• Dermatophytes
• Tinea versicolor (pityriasis versicolor)
• Tinea nigra
• Piedria hortae (black piedra)
• Subcutaneous mycoses:- subcutaneous
tissue---progressive local diseases---tissue
destruction
Source:- saprophytic fungi of soil, decaying vegetation
penetrate into abraded skin
• Mycetoma
• Sporotrichosis
• Rhinosporidiosis
Subcutaneous mycoses
• Systemic mycoses are fungal infections
affecting internal organs. In the right
circumstances the fungi enter the body via the
lungs, through the gut, paranasal sinuses or
skin.
Source:- fungal spores in soil----- inhalation
• Blastomycosis
• Histoplasmosis
• Cryptococcosis
• Coccidioidomycosis
• Paracoccidioidomycosis.
• Deep mycosis:- systemic + subcutaneous
• Opportunistic mycoses
Saprophytic fungi causes opportunistic infections
in immunocompromised individuals, cancer
therapy, immunosuppresive agents, chronic
diseases.
• Candida albicans-endogenous infection.
• Aspergillus
• Zygomycosis
• penicillosis
Opportunistic mycoses
Specimen collection & Transport
• Proper specimen collection & prompt transport of
specimens
• Liquid or moist specimens collected in screw capped
sterile containers – sputum, Bronchial washings, CSF,
urine & Exudates
• Skin scrapings, nail fragments, hairs, corneal
scrapings transported in an envelope or Petridish
• Tissue biopsies transported in screw capped container
with sterile saline
• Blood – Blood culture bottles containing Brain Heart
infusion broth
Laboratory diagnosis of
fungal infections
• Direct Microscopy
• Culture
• Histopathology
• Serodiagnosis
• Antifungal sensitivity testing
Direct microscopy
Wet mounts
– KOH- 10%
– India ink – capsule demonstration
1. 10%
2. KOH with calcofluor white or
Acridine orange
• Fungal elements fluoresce
3. India Ink preparation / Nigrosin
stain
Detection of capsulated yeast
Eg: Cryptococcus neoformans
Staining methods
• Gram staining
• Modified Acid-Fast stain
• Giemsa stain – Histoplasma Capsulatum
• Grocott – Gomori’s Methenamine silver stain
• Fluorescent – antibody staining – systemic fungal
infections – detection of fungal antigen in clinical
material
• Biopsy specimens – H&E stain, PAS stain & Mayer’s
Mucicarmine stain (C. neoformans & Rhinosporidium)
Culture
SDA
–Sabouraud’s dextrose agar –
basal medium
– Sabouraud’s dextrose agar + antibiotics
– Culture media incubated at 250C & 37 0C for 3
– 4 wks.
Identification of growth
• Gross appearance
– Rapidity of growth
– Colour & morphology of the colony on obverse &
pigmentation on reverse
• Microscopic appearance
– Fungal isolates identified by microscopy
• Biochemical tests & special tests
Microscopic identification of
fungal isolates
LPCB contains lactic acid, phenol & cotton blue
for study of morphology of fungi ,to detet fungal
spores
Yeasts
Serological tests
• Latex agglutination –
• Immunodiffusion
• ELISA
• Molecular methods-
- PCR
Antifungal agents
Amphotericin B
Ketoconazole
Fluconazole
Itraconazole
SLOs of the topic:
1. summarize general properties, structure and growth of
fungi
2. explain basic approach for classification of human
pathogenic fungi
3. brief general description of transmission and
pathogenesis of fungal diseases
4. explain the approach for diagnosis, treatment and
prevention of fungal infections
5. Enumerate the different specimens collected
6. List the methods for diagnosis of fungal pathogen from
the clinical specimen
QUESTIONS TIME
1. Mention the morphological classification
of fungi with examples
2. Mention the broad classification of fungal
infections based on clinical presentation
with examples
3. List the routine laboratory investigations
for fungal infections
WHICH FUNGUS IS THIS?
