Mycology I Flashcards
_____ is a sterol component of fungal cytoplasmic membranes. It is similar in structure to cholesterol, but different enough to be the target of anti-fungal therapies.
Ergosterol
_____ is a polysaccharide polymer that gives fungal cell walls structural integrity & rigidity.
Chitin
_____ are sugars with mannoproteins embedded in them. They face the external environment and are antigenic.
Glucans
Fungi have two morphological forms in their growth. _____ are unicellular, and exhibit budding reproduction. Their structural unit is the _____, which buds from the mother cell and detaches.
Fungi have two morphological forms in their growth. YEASTS are unicellular, and exhibit budding reproduction. Their structural unit is the BLASTOPORE, which buds from the mother cell and detaches.
Fungi have two morphological forms in their growth. _____ are charactrerized by their fuzzy appearance due to their hyphae, and their spores/conidia.
Fungi have two morphological forms in their growth. MOLDS are charactrerized by their fuzzy appearance due to their hyphae, and their spores/conidia.
Note: Filamentous fungi generate these spores through asexual reproduction. Filamentous fungi are also difficult to phagocytize.
_____ hyphae have pores between cells that allow communication.
Septate hyphae
_____ hyphae have no divisions and are therefore continuous with multiple nuclei floating freely within the “tube”.
Aseptate hyphae
_____ are a type of fungal spore characterized by spores coming off an acentral structure, having a Mardi Gras bead-like appearance.
Conidiophore
_____ are a type of fungal spore characterized by spores enclosed in a sac.
Sporangium
_____ are a type of fungal spore produced by the segmentation (fragmenting off) of hyphae.
Anthroconidia
What are the four species of dimorphic fungi presented in our lecture?
Histoplasma capsulatum
Blastomyces dermatitidis
Coccidiodes immitis
Paracocciodes brasiliensis (more tropical)
Dimorphic fungi exist as _____ in the ambient temperature of the external environment and as _____ once inside a human host and exposed to body temperature. Why is this the case?
Dimorphic fungi exist as FILAMENTOUS FUNGI in the ambient temperature of the external environment and as YEASTS once inside a human host and exposed to body temperature.
This is because filamentous fungi are hard to phagocytize, while yeasts are more readily phagocytized. Once phagocytized, yeasts can exist as an intracellular organism, allowing their protection from human innate immunity.
_____ are commonly thought of as commensals on mucosal surfaces. Their population is kept in check by T cell mediated immunity. When there is immunosuppression or a change in environment, these fungi can infect the vaginal tract and blood stream, and can cause systemic infections.
Candida
IDing fungi in the lab can be done with many different techniques. Wet mountinga tissue sample with _____ will digest human cells, leaving behind only fungal elements.
10% KOH
Under the correct wavelength of light, fungi will glow from staining with _____
Calcofluour white
Staining with _____ will stain fungal elements blue, helping to determine whether a fungus is septate or aseptate.
Lactophenol cotton blue
Fungi can be inoculated on _____ or _____ to ensure proper diagnosis. What’s special about these agars?
Sabouraud’s agar or mycosel
These agars are special because they contain antibiotics to suppress growth of normal skin flora. They may also have cyclohexamide to retard growth of non-pathogenic fungi.
What are the two kinds of polyenes? How are they applied?
Amphotericin B - Systemic/oral
Nystatin - Topical
What is the mode of action for polyenes?
1) Bind ergosterol, forming a pore to kill fungi
2) Form ion channels
These are broad spectrum mechanisms, that are effective against BOTH yeasts and molds
What are fungi’s mechanism of resistance for polyenes?
1) Reduce amount of ergosterol in membranes
2) Replace ergosterol with fecosterol (does not bind amphotericin B with same avidity)
Flucytosine (5-fluorocytosine) is converted to 5-fluorocil by _____. It enters the fungal cell via _____
Flucytosine (5-fluorocytosine) is converted to 5-fluorocil by CYTOSINE DEAMINASE. It enters the fungal cell via PERMEASE.
What is the mode of action for Flucytosine?
After its conversion to 5-FU, it competes with uracil in RNA synthesis, blocking it.
5-FUMP also interferes with thymidylate synthetase and DNA synthesis.
What are fungi’s mechanisms of resistance against Flucytosine?
1) Mutate permease
2) Mutate cytosine deaminase
Imidiazoles have _ N in the azole ring, while triazoles have _
Imidazoles - 2N in azole ring
Triazoles - 3N in azole ring
What is the mode of action for azoles?
Azoles block the enzyme 14-alpha demethylase, which converts lanosterol to ergosterol. This leads to accumulation of toxic sterols in the membrane.
What are fungi’s mechanism of resistance against azoles?
1) Efflux of drug out of cell faster than influx
2) Alteration of enzyme (14-alpha demethylase) so that it no longer binds azoles
_____ are antifungals that are high molecular weight lipopeptides. They reduce the amount of amphotericin B needed, and are not as toxic.
Echinocandins
What is the mode of action for echinocandins?
Echinocandins interfere with the synthesis of Beta-1,3-glucans.
Mammals do not have this , therefore echinocandins are relatively non-toxic
What are fungi’s mechanism of resistance against echinocandins?
Target alteration (alteration of beta-1,3-glucans
What is the mode of action for allylamines?
Inhibit squalene epoxidase, which is needed to make ergosterol
Allylamines are _____, making them able to penetrate the skin. This makes them particularly effective against fungal infections of skin, hair and nails.
Lipophilic
What are fungi’s mechanism of resistance against allylamines?
Active efflux out of the cell
_____ is an antifungal commonly given orally to children with ringworm. It interferes with microtubules in fungal cells such that they cannot complete mitosis.
Griseofulvin
_____ is an antifungal that distorts hyphae and stunts mycelial growth. Like allylamines, it also inhibits squalene epoxidase.
Tolnaftate
_____ is characterized by short branched hyphae and thick walled yeast-like cells, giving it a “spaghetti and meatballs” appearance.
Pityriasis/Tinea Versicolor
Seborrheic dermatitis (similar to dandruff) is caused by _____ infection. This fungus likes to live in high lipid areas, where you sweat the most.
Pityriasis/Tinea Versicolor
Treatment for Pityriasis/Tinea Versicolor?
Topical/oral azoles or selenium sulfide, though, as a superficial infection, they don’t do much damage.
Superficial infections of the hair causes the condition known as _____
Tx?
White Piedra
Tx: topical azoles, improve hygiene, shave
White piedra is caused by the fungus _____
Trichosporon cutaneum
T/F: Cutaneous mycoses are limited to the upper layers of skin and do not illicit an inflammatory response.
FALSE
Though they are limited to the upper layers of skin, cutaneous mycoses CAN illicit an inflammatory response.
Three genus of fungi causing cutaneous mycoses?
1) Trichophyton
2) Epidermophyton
3) Microsporum
Four species of trichophyton causing cutaneous mycoses? Which is most aggressive?
1) Rubrum (most aggressive)
2) Mentagorophytes
3) Tonsurans
4) Verrucosum
What is the characteristic appearance of T rubrum on agar?
White appearance on top, red coloration underneath.
Which genus, causing cutaneous mycosis, is characterized by smooth walled macroconidia, NO microconidia, does not infect hair, and has the appearance of cigars with septae?
Epidermophyton
Three species of microsporum?
1) Canis
2) Gypseum
3) Fulvum
_____ macronidia are numerous, large, rough and thick walled. Micronidia are rare, and DO NOT INFECT NAILS.
Microsporum
Three classes of cutaneous mycoses?
1) Geophilic
2) Zoophilic
3) Anthropomorthic
Tinea corporis (ringworm) is most commonly caused by anthropomorphic _____, but also by zoophilic _____
T. rubrum
Microsporum
_____ is the most common dermatophyte. It starts with itching between the toes and develops into vesicles that rupture, causing the skin to peel.
Tinea Pedis (Athlete’s foot)
_____ has a typical ringworm appearance, does NOT affect the scrotum like Candida, has lesions defined on the inner thigh that expand centrifugally and are often pruritic. They typically spread from person to person.
Tinea cruris (Jock itch)
_____ is an infection of the hair shaft caused by microsporum that grows on the OUTSIDE of the hair shaft.
_____ is an infection caused by trichophyton that grows WITHIN the hair shaft.
ECTOTHRIX - microsporum - outside of hair shaft
Endothrix - trichophyton - outside of hair shaft
A _____ is an infection of hair follicles in the scalp or beard, caused by trichophyton and microsporum. They have a raised spongy appearance and can be accompanied by a secondary staph infection. These are found most commonly with what kind of fungal infection?
Kerion - Tinea capitis and barbae
In _____, the nails become thickened, discolored, friable and/or deformed. They are most commonly caused by _____, but other fungi as well.
Tinea Unguium
Most commonly caused by T rubrum
_____ work well against dermatophytes regardless of genus.
Topical azoles (though oral work as well)
_____ are caused by fungi that live in soil or on vegetation. They require _____ to bypass intact skin.
Subcutaneous mycoses
Require trauma!
_____ is caused by Sporothrix schenckii, a dimorphic fungus.
Lymphocutaneous sporotrichosis
_____ causes lymphocutaneous sporotrichosis. At ambient temp is a _____, at body temp, it is a small pleiomorphic _____.
SPOROTRIX SCHENCKII causes lymphocutaneous sporotrichosis. At ambient temp is a MOLD, at body temp, it is a small pleiomorphic YEAST.
