Medical Mycology

Dr Gopisankar M G

• Fungi has been recognized as disease causing even before bacteria

• Favus Trichophyton schonleinii

• Thrush Candida albicans

• Most Fungi are soil saprophytes

• Infections are mostly opportunistic

Fungi

• Eukaryotic Protista

• Rigid cellwall chitin , mannan and other polysacharides

• Cytoplasmic membrane contains sterols

• Possess true nuclei ,with nuclear membrane and paired chromosomes

• Divides sexually asexually and both

• May be unicellular or multicellular

• The cells show various degrees of specialisation

• Simplest unicellular budding yeast

• Elongation of cell produces a tubular thread like structure called hypha

• Tangled mass of hypha is called mycelium

• Fungi which forms mycelium is called moulds or filamentous fungi

• Hypha may be septate or non spetate

• Septa has hole through it

• Mycelium can be vegetative or aerial

• Vegetative grows into the medium

• Aerial grows from the surface

Based on morphology

1. Yeasts

2. Yeast like Fungi

3. Moulds

4. Dimorphic Fungi

Yeasts

• Unicellular fungi

• Spherical or ellipsoid cells

• Reproduce by budding

• Culture forms smooth , creamy colonies

• Only pathogenic yeast Cryptocoocusneoformans

Yeast like fungus

• Grows partly as yeasts and partly as elongated cells resembling hyphae

• Such hyphae form psuedomycelium

• Eg is Candida albicans

Moulds /Filamentous fungi

• Forms true mycelia

• Reproduce by spores

•

• Eg Dermatophytes

Dimorphic Fungi

• Can occur as filaments or as yeasts

• Depending on the condition of growth

• In hot tissues or cultures as yeasts @37C

• In soil and in cultures @22C they appear as asmoulds

• Most Fungi causing systemic infections are dimorphic fungi

Based on spore formation

1. Phycomycetes

2. Ascomycetes

3. Basidiomycetes

4. Fungi imperfecti

Phycomycetes

• Lower fungi

• Non septate hyphae

• Form endogenous asexual spores (sporangiospores)

• Contained in swollen sac like structures called sporangia

• Sexual spores oospores/zygospores

• Other 3 have septate hyphae

• And they have exogenous asexual spores conidia

Ascomycetes

• Sexual spores Ascospores within a sac or ascus

• Includes

1. Yeast

2. Filamentous fungi

Basidiomycetes

• Sexual spores Basidiospores

• On a basidium or base

Fungi imperfecti

• Deuteromycetes / hyphomycetes

• Sexual phase has not been identified

• Fungi of medical importance belongs here

Lab diagnosis

• Microscopy

• 10% KOH

• Lactophenol cotton blue

• Slide culture

• PAS / Methanamine silver stains for fungal elements in tissue sections

Culture media

• Sabouraud’s glucose agar (PH 5.4)

• Czapek- ox medium

• Corn Meal agar

• Addition of antibiotics

• Cycloheximide inhibits many contaminentmoulds

• 22C for weeks /37 C for days

• Identified by morphology

identification

• Rapidity of growth

• Colour of colony

• Morphology of colony

• Pigmentation

Eg

• Spring like helical coils spiral hyphae

• Localised swellings formed by tightly twisted hyphae resembling tennis racquets Raquethyphae

• Numerous short branches appearing at the end of hyphae favic chandlier

conidia

• Small and single micrconidia

• Large single or multi celled Macroconidia

Type of spore formation

• Blastospores by budding as in yeasts

• Arthrospores along the mycelium by segmentation and condensation of hyphae

• Chlamydospores thick walled resting spores formed by rounding up and thickening of hyphal segments

Mycoses / Fungal infections

• Superficial

• Systemic/deep

• Opportunistic

Superficial mycoses

• Surface infections

• Cutaneous infections

Superficial

• Only in the dead layers of skin

• No inflammatory response

• Only cosmetic problems

1. Pityriasis Versicolor / Tinea versicolor

2. Tinea Nigra

3. Piedra

Cutaneous

• Dermatophytosis

1. Trichophyton

2. Microsporum

3. Epidermophyton

Both

• Candidiosis

Deep mycosis

1. Subcutaneous

a. Mycotic Mycetoma

b. Chromoblastomycosis

c. Sporotrichosis

d. Rhinosporidiosis

e. Subcutaneuos phycomycosis

“RHINO CHROMO SPORO MYCO PHYCO”

2. Systemic mycoses

a. Cryptococcosis

b. Blastomycosis

c. Paracoccidiodomycosis

d. Coccidiodomycosis

e. Histoplasmosis

Opportunistic systemic

• Aspergillosis

• Penicillinosis

• Mucormycosis

• Otomycosis

• Oculomycosis

Mycotic Poisoning

1. Mycetism

psilocybe

a. Mycotoxicosis

Aspergillus flavus ,

Claviceps purpurea