Introduction to Fungal Pathogens Flashcards
Fungi may reproduce by ____ and/or ____ means, and the nature reproduction is used in classification.
sexual; asexual
Like plants, fungi have _____, a feature which separates them from animals. They contain chitin (a material also found in the exoskeleton of insects) and also cellulose (a material found in plant matter).
rigid cell walls
Fungi also have a cell membrane inside of the cell wall which contains _____.
ergosterol
Fungal species may be subclassified as ____, _____, _____, or _____.
saprobes, symbionts, commensals, or parasites
_____ live upon dead and decaying organic matter.
Saprobes
_____ live upon another organism to the mutual advantage of both.
Symbionts
Like plants, fungi have rigid cell walls, a feature which separates them from animals. They contain ____ (a material also found in the exoskeleton of insects) and also _____ (a material found in plant matter).
chitin; cellulose
_____ live upon another organism with no detriment to the host.
Commensals
Colonies of yeast are usually ____ or ____ in appearance.
moist; mucoid
Fungi also have a ____ inside of the cell wall which contains ergosterol.
cell membrane
What is a sapbrobe?
fungi that lives upon dead and decaying organic matter
_____ live upon another organism with clear detriment to the host.
Parasites
Fungi occur in two basic growth forms:
- yeast
2. molds
What is a symbiont?
fungi that lives upon another organism to the mutual advantage of both
YEAST - a _____ growth form where the fungus reproduces via budding to form _____, or by dividing in half through fission.
unicellular; blastoconidia
What are Commensals?
fungi that live upon another organism with no detriment to the host
Parasites are?
fungi that live upon another organism with clear detriment to the host
Medically relevant yeast includes ____ and ____.
Cryptococcus neoformans; Candida albicans
MOLDS - a _____ growth form where the fungus reproduces via formation of _____.
filamentous; spores or conidia
The filamentous elements in mold are called ____.
hyphae
A mass of hyphae is referred to collectively as ____.
mycelium
Medically relevant molds include ____ and _____.
common dermatophytes; Aspergillosis
Pseudohyphae are simply ____; they do not have _____.
elongated yeast linked together like sausages; cytoplasmic connections between the compartments
_____ is an organism that often forms pseudohyphae.
Common Candida albicans
Fungi that do not have a fixed morphology but may exist in a yeast or hyphal form are referred to as ____.
dimorphic
What triggers a dimorphic fungi to transition from one form to another?
an environmental change (atmosphere, temp, or food supply)
Name the medically-relevant thermally dimorphic organisms.
S – some Sporothrix schenckii C – can Coccidioides immitis H – have Histoplasmosa capsulatum B – both Blastomyces dermatitidis P – phases Paracoccidioides brasiliensis
_____ are a specialized from of hyphal elements that grow like roots from larger hyphae.
Rhizoids
____ are those that demonstrate complete cell walls that subdivide the hyphae into compartments.
Septate hyphae
_____ is an example of a septate hyphal fungus, as are the _____.
Aspergillus fumigatus; dermatophytes
What are conidia?
asexual spores borne off specialized aerial hyphae called conidophores
A conidium may be _____ or ____.
large and multinucleated; small and unicellular
What are the asexual spores called?
endospores
What are chlamydospores?
thick walled, round spores that are highly resistant to adverse environmental conditions
_____ form at the ends of hyphae, while ____ form along and within hyphae.
Terminal chlamydospores; intercalary chlamydospores
What are arthrospores?
similar to chlamydospores but more numerous and elongated and likened to a barrel
How does Coccidioides immitis cause disease?
by inhaling the spores
What are spherules?
large, asexual spores that develop during the yeast phase of some organisms
The yeast form of the dimorphic fungus _____ forms spherules in tissue that are filled with endospores.
Coccidioides immitis
What are blastoconidia?
yeasts that bud asymmetrically
What are thick-walled, round spores that
are highly resistant to adverse environmental conditions called?
chlamydospores
These are large, asexual spores that develop during the yeast phase of some organisms.
spherules
What are sclerotic/Medlar bodies?
thick-walled, environmentally protective forms of yeast
What is a thallus?
a fungal colony growing on a culture dish
What is the top side of the growing thallus called?
the obverse side
What is the bottom side of the thallus called?
the converse side
Define anthropophilic.
confined to humans and less inflammatory
Define geophilic.
fungus found in soil
Define zoophilic.
fungus found in animals
Define dematiaceous.
fungus that produces its own pigment (usu melanin)
Name 3 superficial fungal infections.
- tinea
- candida
- pityrosporum
Name several deep/systemic fungal infections.
Sporotrichosis Cryptococcosis Coccidioidomycosis North American Blastomycosis Histoplasmosis Paracoccidiodomycosis Lobomycosis Mucormycosis
What are dermatophytes?
fungi that utilize keratin as a substrate for growth (limits them to the hair, skin, and nails)
What is candida?
non-dermatophyte yeast that prefers the glucose of interstitial fluids for growth
What is pityrosporum?
non-dermatophyte yeast that prefers breakdown products of sebum for growth
The ____ are characterized by their ability to cause systemic infection and usually begin infection in the lungs.
deep mycoses
A patient with itching and scaling between the toes, who also frequents a local health club, and who’s condition has responded in the past to topical antifungal
creams likely has?
“Athlete’s foot” (tinea pedis)
An AIDS patient with headache, mental confusion, and disseminated papules on the skin very likely has _____.
systemic cryptococcosis
How are fungi examined by microscopy?
- take scraping of the epi
- add a drop of KOH or DMSO to clean the fungus of the human components
- maybe add chlorazol E black stain
- observe
How is cryptococcosis viewed via microscopy?
CSF from a lumbar puncture is mixed with India ink, which stains everything EXCEPT cryptococcosis’ mucoid capsule
What is the advantage of doing a fungal culture?
it allows for direct speciation of the infecting organism
_____ is often used on fungal specimens taken from colonies grown via culture.
Lactophenol cotton blue stain
_____ bind with ergosterol in the fungal cell membrane; they are considered to be fungicidal, leading directly to fungal cell death.
Polyenes
____ binds to ergosterol, creating a pore in the fungal
membrane, which causes ions and other molecules to leak out of the cell.
Amphotericin B
Name the polyenes.
- Amphotericin B
2. Nystatin
_____ is another polyene used topically for Candida infections, although it is not absorbed when given by mouth and is too toxic for intravenous use.
Nystatin
The imidazole and triazole antifungals inhibit the
enzyme, 14α-demethylase, the enzyme that converts lanosterol to ergosterol; these drugs are considered to be ____.
fungistatic
The _____ inhibit the enzyme, 14α-demethylase, the enzyme that converts lanosterol to ergosterol; these drugs are considered to be fungistatic.
imidazole and triazole antifungals
Oral imidazoles and triazoles also often interfere with _____, leading to potentially fatal drug interactions with certain medications.
cytochrome P450 enzymes
Name an oral imidazole.
ketoconazole
____ and _____ inhibit the enzyme squalene epoxidase, leading to accumulation of squalene within the fungal cell; this is toxic, making these agents fungicidal.
Allylamines; benzylamines
The most common allylamine is _____.
terbinafine
What is an issue with terbinafine?
it can unmask a lupus-like condition
Which agents inhibit the synthesis of glucan in the cell walls of some fungi, probably via inhibition of the enzyme 1,3-β glucan synthase?
the Echinocandins
In addition to fungicidal activity against _____, echinocandins are fungistatic against _____ but are not useful against many other forms of fungus.
Candida; Aspergillus
_____ inhibits fungal cell mitosis by disrupting mitotic spindle formation, a critical step in cellular division.
Griseofulvin
______ is a small molecule that is transported into fungal
cells by cytosine permease and is then converted in the
cytoplasm by cytosine deaminase to 5-fluorouracil (5-FU). 5-FU is a pyrimidine anti-metabolite that interrupts DNA synthesis.
Flucytosine
_____ is thought to chelate polyvalent metal cations, such as Fe3+ and Al3+ leading to inhibition of many different fungal enzymes, including cytochromes.
Ciclopirox olamine
A 64 year old man presents with an erythematous rash in the groin area
- bright red erythema of the penis and scrotum
- some satellite pustules
- patient states due to his prostate condition his under- pants are often wet, and he wears occlusive absorbent undergarments.
Dx? Tx?
dx: Candidiasis
tx: Air drying, avoidance of prolonged wetness, blood sugar control, topical azoles, nystatin, or oral fluconazole
A 51 year old man, otherwise healthy, presents with a pruritic macerated rash in the groin area. On inspection, you identify erythematous annular plaques of the thighs largely sparing the scrotum. The patient frequents an athletic club and states some of the other
members who he often associated with have had “jock itch.”
Dx? Tx?
dx: Tinea cruris (dermatophytosis)
tx: socks on before underpants, topical azoles or allylamines
A 44 year old bone marrow transplant candidate develops fever, cough, dyspnea, chest pain and hemoptysis while neutropenic and before engraftment. Imaging reveals infiltrates in his lungs. Skin lesions develop with central necrosis. A skin biopsy contains hyphal elements with “acute angle branching” and vascular invasion.
Dx? Tx?
Dx: Aspergillosis
Tx: Voriconazole, posaconazole, amphotericin, or echinocandins, along with a reduction in the dose of immunosuppressives or reversing neutropenia with granulocyte colony-stimulating factors (G-CSF/GM-CSF)
