Mycology Flashcards
Which domain do fungi belong to?
Eukarya
What distinguishes fungi from plants?
There lack of chlorophyll
What are the 3 different classifications of fungi?
Unicellular (yeasts)
Filamentous (moulds)
Dimorphic
What are the characteristics of unicellular fungi (yeasts)?
Facultative anaerobes
Reproduce asexually by budding
Produce colonies on agar
What are the characteristics of filamentous fungi (moulds)?
Aerobes
Reproduce by conidia (asexual spores)
Produce mycelia on agar
What is the appearance of yeast cells in a Gram stain?
Look like Gram positive cocci, but they’re much bigger.
They also undergo budding, which isn’t present in bacteria.
What is the appearance of yeast cells on blood agar?
Look like non-haemolytic streptococcus due to the small colonies, but you can tell them apart because of the yeasty smell.
How does penicillium spp. appear on agar?
As a filamentous fungus with hyphae and conidia.
Which dye is used to visualise penicillium spp. grown on agar?
Cotton blue
What are conidia involved in?
Replication
Is penicillium spp. a yeast or a mould?
Mould
True or false: most fungi are saprophytes.
True
Why are dimorphic fungi best adapted to grow in tissues?
Because they can grow as filamentous fungi in the environment and as yeast when they invade – can switch and grow at 37 degrees, unlike most fungi
Where is histoplasma capsulatum found?
In caves
What type of a fungus is histoplasma capsulatum?
Dimorphic
Which fungi are primary pathogens?
Dimorphic fungi
Dermatophytes
What type of a fungi is ringworm?
Dermatophyte
What is the difference between dermatophytes and agents of subcutaneous mycoses?
Agents of subcutaneous mycoses are low grade pathogens, but anyone can get infected by them.
Innoculated directly into skin, cf. Dermatophytes grow on the skin (love keratin) that don’t invade deeply
Which fungi can cause deforming lesions, e.g. on feet?
Agents of subcutaneous mycoses
Which fungi give the biggest problems in medicine?
Opportunists, due to the increasing number of immunocompromised patients.
Which type of fungi are the poisonous mushrooms?
Toxic fungi
What do toxic fungi produce?
Toxins, e.g. aflatoxin (potentially carcinogenic)
Which common disease to the dermatophytes cause?
Tinea
What do different species of dermatophytes prefer?
Different hosts and tissues
Do dermatophytes often cause infections in humans?
No
Rarely cause infections of humans
What do dermatophytes live off?
Live off shed things, like hair and nails
Where do human-specific dermatophytes grow?
In hair and release by-products, which we react to
What is ringworm’s proper name?
Tinea corporis
In which order do ringworm lesions heal?
From the inside and spread
What does scaling in tinea result from?
The patient reacting to the metabolites created by the dermatophyte.
Where is tinea cruris?
Near the groin
Where is tinea pedis?
Feet
Where is tinea capitis?
Scalp
Where is tinea unguium?
Nails
What is mycetoma also known as?
Maduromycosis
What are the two types of mycetoma (maduromycosis)?
Bacterial and fungal
What is bacterial mycetoma called?
Actinomycetoma
What is an example of a bacterial mycetoma?
Nocardia spp.
What does Nocardia spp. cause?
Actinomycetoma
True or false: only actinomycetes will cause actinomycetoma.
True
What is fungal mycetoma also referred to as?
Eumycetoma
Which species will cause fungal mycetoma (eumyctoma)?
Madurella spp.
What is special about mycetoma (maduromycosis)?
One of the few conditions than can be caused by a bacterium or a fungus, important because bacteria and fungi are susceptible to totally different antimicrobials – there’s no overlap.
Why can’t we use antibiotics that kill both bacteria and fungi?
Because they’ll also kill us because they have low selective toxicity
What is characteristic of mycetomas?
Sulphur granules and yellow discharge
What is present in the sulphur granules of mycetomas?
Inflammatory cells
What kind of bacteria are present in the actinomycetoma granules?
Branching bacteria
What is present in the eumycetoma granules?
Filaments and hyphae with septa between the hyphae cells
What are some examples of subcutaneous mycoses?
Mycetoma
Chromoblastomycosis (chromomycosis)
Phaeohyphomycosis
What are some examples of opportunistic mycoses?
Candidiasis (Candida albicans)
Cryptococcosis
Aspergillosis
What causes candidiasis?
Candida albicans
What are the 3 different types of candidiasis infections?
Mucocutaneous candidiasis
Chronic mucocutaneous
Systemic
What is mucocutaneous candidiases?
Infection of the mucous membranes and skin (often both)
What group of people get chronic mucocutaneous candidiasis?
People who have specific but different kinds of immune defects that don’t allow them to get rid of candida, so when they get infected, it becomes chronic.
What is systemic candidiasis?
The fungus invades, causes septicaemia and is often fatal
What group of peoples is systemic candidiasis often seen in?
Neonates
Patients with advanced immunodeficiency, e.g. severe AIDS
What are the 2 agents that cause cryptococcus in humans?
C. neoformans
C. gattii
What is the most common cause of cryptococcus in humans?
C. neoformans
Which diseases will cryptococcus cause?
Pulmonary infection
Meningitis
How does the fungus enter the system in pulmonary infections involving cryptococcus?
Inhaled
What is cryptococcal meningitis synonymous with?
Fungal meningitis
What is cryptococcus’ relationship with AIDS?
Cryptococcal infection is an AIDS-defining illness
How does cryptococcal meningitis present?
Insidious, people complain of headaches, but if nothing is done it will kill the person
What feature of cryptococcus contributes to its virulence?
Massive capsule
What do the bacteria that cause meningitis have in common?
They are all encapsulated
How does aspergillosis occur?
Grows as a saprophyte in the tissue by infecting a pre-existing cavity (e.g. from cavitating TB) after being inhaled.
How will aspergillosis in a patient who has had cavitating TB appear on X-ray?
It will look like cancer in the apex of the lung
How do you know if the treatment for the infection is working?
Using antigen detection (latex agglutination)
If antigen is going down, treatment is working.
What does intact cell mass spectroscopy (IC-MS) detect?
Unique biomarkers or patterns in whole bacteria or fungi
What are the anti-fungal chemotherapy drug classes used to treat systemically?
Polyenes
Triazoles
Echinoandins
5-fluorocytosine
What is an example of a polyene used for systemic chemotherapy treatment?
Amphotericin B
What is an example of a triazole used for systemic chemotherapy treatment?
Fluconazole (1st gen)
Voriconazole (2nd gen)
What is an example of a echinocandin used for systemic chemotherapy treatment?
Capsofungin
What are the topical anti-fungal chemotherapies?
Polyenes e.g. nystatin
Imidazoles e.g. clotrimazole
What are the 2 targets of anti-fungals?
Ergosterol
Nucleic acids
What is the ergosterol?
Found in cytoplasmic membrane of fungi (like cholesterol in our membranes)
What effect do polyenes have on ergosterol?
Affect integrity - bind with higher affinity to ergosterol than cholesterol, but also bind cholesterol – these are the best antifungals available.
What effect do allylamines, triazoles, morpholines have on ergosterol?
Affect ergosterol synthesis
What is the MoA of 5-fluorocytosine?
Affects DNA and RNA synthesis
Can humans be affected by 5-fluorocytosine?
No
Humans can’t activate the drug, but fungi can.
What is used to treat Candida spp.?
Fluconazole
Amphotericin B
Caspofungin
What is used to treat cryptococcus?
Amphotericin B
5-fluorocytosine
What is used to treat aspergillus?
Voriconazole
Amphotericin B
What is used to treat dimorphic fungi?
Amphotericin B
What doesn’t treatment of dermatophytosis require?
Amphotericin B
What is a non-specific treatment of dermatophytosis?
Reduce fungal load
What are the 3 topical treatments for dermatophytosis?
Terbinafine (“Lamisil”)
Clotrimazole (“Canesten”)
Amorolfine (“Loceryl”)
When is treatment of dermatophytosis with oral medications done?
Only if it’s difficult to treat topically or is widely disseminated - also in the nails
What are the 3 oral treatments for dermatophytosis?
Terbinafine
Fluconazole
Griseofulvin
