Mycology Flashcards
What is S.cerevisiae?
Baker’s yeast
Describe the classification of fungi?
Unicellular (yeasts)
Filamentous (moulds)
Dimorphic
Describe the basic properties of yeasts and moulds?
YEASTS
Unicellular, facultative anaerobes, reproduce asexually by budding, produce colonies on agar
MOULDS
Filamentous, aerobes, reproduce by conidia, produce mycelia on agar
What is a conidium?
What is a mycelium?
Conidia: asexual spores
Mycelia: mass of branched, tubular filaments of fungi
Describe the appearance of yeast cells on a Gram stain?
Larger than bacteria
Look like strange Gram positive cocci
Budding visible
Describe the appearance of yeast culture on blood agar?
Non-descript, small colonies
Yeasty smell
Describe the appearance of filamentous fungus on culture?
Filaments
Describe the features of fungi visible in this picture?
Hyphae and conidia
Rank the virulence fungi types?
Descending order of virulence:
Dimorphic fungi
Dermatophytes
Agents of subcutaneous mycoses
Opportunists
Toxic fungi
Which types of fungi are primary pathogens?
Dimorphic fungi
Dermatophytes
Describe why dimorphic fungi are so virulent?
Best adapted to grow in our tissues: can grow as moulds (filamentous) in the environment, and switch to yeast (unicellular)when they invade us
Give an example of a dimorphic fungus?
Histoplasma capsulitin
Causes Cave’s disease
Give an example of a dermatophyte?
Ringworm fungus
Describe how dermatophytes colonise us?
Grow on skin, hair and nails
Don’t invade deeply
What are agents of subcutaneous mycoses?
Low grade pathogens
Inoculated directly into skin
Which patients do opportunistic fungi affect?
Immunocompromised patients
Give an example of a toxic fungus?
Poisonous mushrooms
Describe the behaviour of toxins released from fungi?
They diffuse
So, don’t just chop the mouldy bit off the cheese!
What do dermatophytes cause in humans?
Tinea
How are dermatophytes classified?
Three genera
Morphologically different, and have preferences for different tissues and hosts
Give an example of a subcutaneous mycosis?
Mycetoma (maduromycosis)
What are the causes of mycetoma?
Can be caused by bacteria (acintomycetoma, eg. nocardia spp.) or fungi (eumycetoma, eg. madurella spp.)
Give three examples of opportunistic mycoses?
What are they caused by?
Candidiasis: candida albicans (yeast)
Cryptococcosis: c.neoformans or c.gattii (yeast)
Aspergillosis: aspergillus spp. (filamentous)
Describe the types of candidiasis?
Mucocutaneous: infects mucous membranes
Chronic mucocutaneous: can’t get rid of it
Systemic: invasive, fatal
In which patients does systemic candidiasis most commonly occur?
Neonates
Advanced immunodeficiency
Why can fungi reach such large numbers in the body?
Can reach large numbers before they kill a patient, because they don’t activate the immune system as strongly as bacteria and viruses
Which agent of cryptococcosis may cause infection in non-immunocompromised individuals?
Why?
C.gattii
More virulent than other agents
What diseases areassociated with cryptococcosis?
Pulmonary infection (inhaled)
Meningitis (if it spreads to blood or if casued by c.gattii)
In which patients does meningitis due to cryptococcosis usually occur?
AIDS (AIDS defining illness)
Lymphomas
High dose steroids
What are the different clinical forms of Aspergillosis?
Saprophytic (fungus ball)
Allergic (can occur at distant site)
Systemic
What can saprophytic Aspergillosis be mistaken for?
Tumour
Large fungus ball resembles a tumour
Which methods can be used to diagnose fungal infections?
Microscopy
Culture
Antigen detection
PCR
Mass spec
What is present in the microscopic image?
Tinea: hyphae in skin scraping
Describe how c.albicans can be detected via culture?
One test to see if it is c.albicans
If not > do a whole lot of other biochemical tests
Which fungus is this?
How can we tell?
Macronidia: Epidermophyton sp.
Unique appearance
What is shown in this image?
Germ tubes (pseudohyphae) of c.albicans in vitro
When is antigen detection often employed for fungi?
Used a lot for pseudococcus
Used to see if treatment is working
What are the two types of anti-fungal chemotherapy?
Systemic
Topical
List the systemic anti-fungal chemotherapies?
Polyenes
Triazoles
Echinocandins
5-fluorocytosine
List the topical anti-fungal chemotherapies?
Polyenes
Imidazoles
What are the targets of anti-fungals?
Ergosterol in cytoplasmic membrane: polyenes affect integrity, allylamines trizoles and morpholines affect synthesis
Nucleic acids: 5-fluorocytosine affects RNA and DNA synthesis
Why must patients on anti-fungal therapies be hospitalised?
To monitor toxicity
Describe the main treatment of the following systemic fungal infections:
a) Candida spp.
b) Cryptococcus
c) Aspegillus
d) Dimorphic fungi
a) Fluconazole
b) Amphotericin B + 5-fluorocytosine
c) Voriconazole
d) Amphotericin B
Which types of treatment can be employed for dermatophytosis?
Non-specific (to reduce fungal load)
Topical
Oral
In which situation would oral treatment of dermatophytosis be used?
If it is difficult to treat topically
If it is widely disseminated
If it is under the nails
