Basic Mycology Flashcards
Basic characteristic of Fungi: cell wall and cell membrane components, classifications
Eukaryotic, ubiquitous
Fungal cell wall glycans: mannan, glucan and chitin
Fungal cell membrane: phospholipid bilayer with ergosterols
(both these are possible targets of antifungals)
Unicellullar –> Yeasts
Multicellular –> Moulds
Dimorphic: change with temperature e.g. candida (yeast-like at 37 degrees, mould-like at 25 degrees)
Yeasts: general staining characteristics (4)
Gram +ve staining
Budding (daughter cell)
Oval shaped (vs round bacteria)
4-5 micrometre (vs 1 micrometre bacterial)
Yeast: Candida - normal sites, growth conditions, morphology (3), diagnosis (2), disease (2)
Candida albicans (and non-albicans)
General characteristics:
- filamentation (pseudohyphae): virulence factor
- commensals of human intestinal tract and vaginal tract
- growth best at 37 degrees, aerobic
- Sabouraoud dextrose agar (4% w/v dextrose) for 48 hrs –> round white colonies, smooth edge, 3-4 micrometers
Morphology: (on unstained wet mount)
- budding
- pseudohyphae (elongated, constriction at budding site)
- true hyphae (elongate through process of apical synthesis that doesn’t involve budding)
Diagnosis:
- GERM TUBE TEST - suspend yeast cells in horse serum at 37 degrees for 2 hrs
- -> germ tube formation +ve in Candida albicans/ -ve in non-albicans
- -> speciation predictive of anti fungal susceptibility results
- KOH wet mount
Disease:
- oral thrush
- candida vulvovaginitis
Yeast: Pneumocystis jirovecii - growth conditions, morphology (2), diagnosis (2), disease (1)
Previously known as pneumocystis carinii and thought to be parasite (trophozoite and cyst forms)
General:
- appear in clusters - CUP SHAPED (collapsed basketball)
- obligate intracellular org –> NON-CULTIVABLE in lab
- no ergosterol
Diagnosis:
- BAL/ induced sputum –> TOLUIDINE BLUE O STAIN
- microscopy: >5/high power field (as org is ubiquitous)
Disease:
- via inhalation
- pneumonia in severely immunocompromised e.g. AIDS
Yeast: Cryptococcus neoformans species complex - morphology (2), variants and their serotypes/ source/ at risk groups (2), diagnosis (1), disease (2)
General:
- unicellular, oval, 5 micrometres
- large extracellular CAPSULE (similar size to a cell)
- wide ecological niche
- capsular polysaccharides serotypes A-D
var. neoformans
- serotypes A/D
- worldwide
- PIGEON FAECES, soil
- immunosuppressed patients e.g. AIDS
var. gattii
- serotypes B/C
- tropics, subtropics
- eucalyptus tree in Australia
- immunocompetent patients, poor prognosis
Diagnosis:
- CSF for INDIA INK (negative stain) –> budding with large capsular halo
- Latex agglutination assay for capsular polysaccharide antigen
Disease:
- via inhalation (aerosolisation of contaminated soil)
- neurotropism –> meningoencephalitis (confusion and fever)
- extra-neural disease is rare e.g. pneumonia, prostate infection
Yeast: Malassezia furfur - normal site (2), biochemical properties, diagnosis (1), disease (1)
Dimorphic, yeast-like
General:
- normal skin flora
- LIPOPHILIC
- associated with sebum (glands in face and upper trunk)
Diagnosis:
- SKIN SCRAPING for KOH preparation and culture (requires olive oil supplement)
Disease:
- superficial skin infections (hyper or hypopigmentation) – Tinea versicolor
KOH wet mount preparation: method, purpose
10% KOH to digest keratin from skin scrapings – blur the cell junctions so filaments easier to visualise
Lactophenol cotton blue counterstain (highlight edge of fungal filaments)
Examine at 10x or 40x objective lenses
–> visualise fungal filaments (differentiate M. furfur, candida and dermatophytes from other skin disorders)
Mould: Zygomycetes - morphology, diagnosis (2), disease
(genus: rhizomucor, muco, rhizopus)
Commonly known as bread mould
Morphology:
- irregular, NON-SEPTATED hyphae
Diagnosis:
- fragile and easily crushed in specimen –> low culture yield (difficult to dx)
- molecular or serological dx
Disease:
- via inhalation, skin infection
- immunocompromised patients e.g. DM, HIV, transplants
- high mortality
Mould: Aspergillus fumigatus - morphology (3), diagnosis (2), disease (4)
Ubiquitous
Morphology:
- SEPTATED HYPHAE
- ACUTE ANGLE BRANCHING
- CONIDIA (spore-like, thick-walled and resist unfavourable conditions)
Diagnosis:
- biopsy for KOH wet mount
- CULTURE: top smoky grey-green with conidia, bottom yellow
(CXR for aspergilloma; IgE)
Disease:
- allergic reactions, aspergilloma, invasive pulmonary infection, aflatoxin (HCC)
Mould: Dermatophytes- pathology, morphology (3), diagnosis (3), disease (1)
Trichophyton, epidermophyton, microsporum
Infects the keratin layer of skin, hair, nail (doesn’t invade into deeper tissue due to inhibition by serum) – not life threatening
Morphology:
- Microsporum: macroconidia (thick-walled, fusiform shape), microconidia
- Trichophyton: macroconida rare, microconidia
- Epidermophyton: macroconidia (smooth, thin-walled), no microconidia
Diagnosis:
- SKIN SCRAPINGS (advancing edge) for KOH and CULTURE
- NAIL CLIPPING (proximal part, subungal) for KOH AND CULTURE
+/- plucked hair at alopecia or scarring areas
Disease:
- superficial skin infections (itchy, red, cosmetic concern, persistent for wks)
- –> Tinea infection
Dimorphic: Sporothrix schenckii - mode of infection, disease (2)
Cutaneous infection
Disease:
- direct inoculation of rose thorns
- sporotrichosis/ Rose Gardener disease – lymphocutaneous spread and lymphangitis
Dimorphic: Talaromyces (penicillium) marneffei - morphology (2), disease
Dimorphic – Yeast at 37 degrees, Mould at 25 degrees
Endemic in SE Asia
Morphology:
- diffusable RED WINE COLOUR pigment (on culture)
- hyphae, conidia
Disease:
- affect HIV seropositive patients
- soil exposure (rainy/ inhalation of conidia)
- skin infection, potentially lethal systemic infection
Geographical mycosis - examples of species (2), morphologies
Histoplasma capsulatum - large round macroconidia
Coccidioides immitis - spherules (daughter cells inside)
–> travel history essential (common in America)
Overall Yeasts, Moulds and Dimorphic
Yeasts
- candida
- pneumocystis jirovecii
- cryptococcus neoformans species complex
Moulds
- Aspergillus fumigatus
- Zygomycetes
- Dermatophytes (microsporum, trichophyton, epidermophyton)
Dimorphic
- sporothrix schenckii
- talaromyces (penicillium) marneffei
Geographical mycosis
