Mycobiology I – Flashcards
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| What are mycoses? |
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| human diseases caused by fungi |
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| What do you call mycoses limited to hair, nail, and skin? |
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| superficial and cutaneous |
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| What are condida? |
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| asexual reproductive strctures produced from the transformation of a vegetative yeast or hyphal cell OR from a specialized conidogenous cell, which may be either simple or complex and elaborate. |
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| What are conidiophores? |
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| conidia formed on specialized hyphae |
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| What do you call small conidia? large, multicellular conidia? |
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| microconidia macroconidia |
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| What's a dematiaceous fungi? |
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| fungi whose cell walls contain melanin, which imparts a brown to black pigment |
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| What is dimorphic fungi? |
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| fungi that have two growth forms, such as a mold and a yeast, which develop under different growth conditions (eg Blastomyces dermatitidis forms hypae in vitro and yeasts in tissue) |
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| What are hyphae? |
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| tubular, branching filaments (2-10 um in width) of fungal cells, the mold form of growth. |
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| Most hyphal cells are seperated by... What's the exception to this rule? |
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| porous cross-walls called septa zygomycetous hyphae are characteristically sparsley septate |
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| What are the different types/forms of hyphae? |
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| vegetative or substrate (anchor the colony and absorb nutrients) aerial hyphae (project above the colony, bear reproductive structures) |
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| What is a mold? |
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| hyphal or mycelial colony or form of growth |
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| What is a mycelium? |
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| mass or mat of hyphae aka a mold colony |
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| What are pseudohyphae? |
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| chains of elongated buds or blastoconidia |
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| What is a spore? |
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| a specialized structure with enhanced survival value, such as resistance to adverse conditions or features that promote dispersion |
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| What is a yeast? |
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| unicellular, spherical to ellipsoid (3-15 um) fungal cells that usualy reproduce by budding |
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| Fungal cell walls contain... |
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| chitin, mannans, and glucans |
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| What is ergosterol? |
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| unique sterol in the cytoplasmic membrane of fungi. Often a target for anti-fungal agents |
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| What is the structural unit of yeast? |
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| blastospore |
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| What determines the different forms of dimorphic fungi? |
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| can be temperature dependent or temperature and nutrition dependent |
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| T/F Fungi are autotrophs. |
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| False! they are heterotrophs |
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| What's the difference between perfect and imperfect fungi? |
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| perfect fungi reproduce sexually imperfect fungi reproduce Asexually |
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| T/F Most fungi that are also human pathogens are pefect fungi. |
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| False, they are imperfect |
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| What are spores that are fragmentation of hyphae? |
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| arthrospores (such as in Coccidiodes) |
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| What is the most common type of spore? |
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| chlamydospore (resting spore) |
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| What do you call a budding spore characteristic of yeast? |
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| blastospore |
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| What is a sporangiospore? |
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| a spore found within a sporangium or sphere (ex. Rhizopus or the tissue phase of Coccidiodes) |
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| T/F Spores can serve as the primary infectious particle and can be antigenic. |
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| true |
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| What are the common pathways of infection for fungi?> |
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| trauma, inhalation, contact (direct or indirect) |
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| How do you ID fungi in the lab? |
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| collect sample, prepare a wet mout in 10% KOH to look for fungal elements, inoculate culture media and incubate plates 1-4 weeks at room temp, serologic testing for fungal antigens, immunoflorescent microscopy |
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| How do you obtain a sample to test for fungi in the lungs? |
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| bronchial lavage fluid (BAL) |
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| What is Calcoflour white? |
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| stains fungal cell walls and causes them to flouresce |
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| Wat are some good culture media for fungi? |
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| Sabouraud's agar, mycosal agar, wet mount with lactophenol cotton blue |
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| What is Sabouraud's agar? |
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| beef extract-dextrose with 5.0 pH to inhibit bacterial growth |
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| What is mycosel agar? |
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| sabouraud's, chloramphenicol and cyclohexamide |
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| Name two antifungal agents that are polyenes? |
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| amphotericin B and nystatin |
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| What is the structure of polyene antifungals? |
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| large lactones ring with a rigid lipophilic chain containing three to seven double bonds and a flexible hydrophilic region harboring several hydroxyl groups (molecule is an amphiphilic rod) -farily insoluble in water and poorly absorbed so it's complexed or enclosed in a lipid |
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| How do polyenes kill fungi? |
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| bind to ergosterol and forms ion channels that destroy osmotic integrity of the fungal cell. Also oxidation of drug generates toxic free radicals which directly damages fungal membrane. BROAD SPECTRUM |
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| What is the mechanism of resistance against polyenes? |
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| resistance is uncommon fungi reduce the amount of ergosterol in membrane or replace ergosterol with fecosterol which binds less amphortericin B |
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| What is another name for flucytosine? |
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| 5-flourocytosine |
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| What's the structure of flucytosine? |
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| an analogue of the pyrimidine cytosine |
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| What is the mechanism of action of flucytosine? |
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| take into the fungal cell by a permease and then converted into 5-flurouricil by an enzyme unique to fungi, cytosine deaminase 5-FU is incorporated into 5-FUMP which then interferes with thymidylate synthetase and DNA synthesis |
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| What is the mechanism of resistance of flucytosine? |
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| mutations in permease, cytosine deaminase result in rapid emergence of resistant mutants (used in combination with other antifungal agents like amphotericin B to increase the efficacy) |
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| Name anti-fungals that are azoles or triazoles? |
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| azoles- imidazole [ketoconazole + 8 others] triazoles- fluconazole, itraconazole, voriconazole, posaconazole |
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| hat is the strucuter of azoles and triazoles? |
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| azoles/imidazoles have 2 nitrogens in the azole ring triazoles have 3 nitrogens in the azole ring |
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| What is the mechanism of action of azoles/triazoles? |
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| interfere with synthesis of ergosterol by blocking demethylation of lanosterol |
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| What fungi are azoles/triazoles effective against? |
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| all azoles are effective against yeast forms of fungi triazoles are effective against Cyrptococcus, candida, histoplasma and blastomyces voriconazole is effective against ALL forms of fungi (including molds) except zygomyces |
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| What are the mechanisms of resistance against the azoles/triazoles? |
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| alter target enzyme to bind less drug or increase target enzyme's expression also, active efflux |
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| What type of drug is caspofungin? |
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| an echinocandins antifungal drug |
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| What is the structure of echinocandins? |
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| high MW semi-synthetic lipopeptides |
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| What is the mechanism of action of an echinocandins? |
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| interfere with the synthesis of beta 1,3 glucans. Since mammalian cells do not have beta-1,3 glucans, caspofungin is relatively non toxic |
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| What is the mechanism of resistance against echinocandins? |
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| mutation in the gene responsible for synthesis of glucans |
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| What is the structure of allylamines? |
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| bicyclic with a long hydrocarbon tail |
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| What is terbinafine? |
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| a systemic allylamine |
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| What is naftifine? |
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| a topical allylamines |
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| What is the mechanism of action of allylamines? |
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| inhibit the enzyme squalene epoxidase, an eenzyme required for erosterol synthesis |
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| Why is terbinafine an excellent drug to use against fungal infections of the skin, hair, and nails? |
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| lipophilic |
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| How do fungi get resistant to allylamines? |
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| active efflux |
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| What is griseofulvin? |
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| an antifungal that disrupts microtubules and interferes with cell division works on dermatophytes only |
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| What is tolnaftate? |
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| a derivative of naphthiomate, works on dermatophytes only |
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| Name some superficial mycosis. |
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| pityriasis versicolor, tinea nigra, white piedra, and black piedra |
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| What causes pityriasis versicolor? |
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| malassezia species |
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| What causes tinea nigra? |
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| hortaea wenickii |
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| What causes white piedra? |
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| trichosporon species |
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| What organisms cause dermatophytosis? |
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| microsporum species, trichophyton species, and epidermophyton floccosum |
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| What causes candidiasis of skin, mucosa or nails? |
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| candida albicans and other candida species |
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| Name examples of cutaneous mycosis. |
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| dermatophytosis |
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| Name examples of cutaneous mycosis. |
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| dermatophytosis |
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| Name an example of a subcutaneous mycoses. |
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| sporotrichosis |
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| Name examples of endemic mycoses. |
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| coccidioidomycosis, histoplasmosis, blastomycosis |
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| What causes sporotrichosis? |
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| sporothrix schenckii |
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| What causes coccidioidomycosis? |
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| coccidioides immitis |
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| What causes histoplasmosis? |
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| histoplasma capsulatum |
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| What causes blastomycosis? |
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| blasomyces dermatitidis |
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| Name examples of oportunistic mycoses. |
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| systemic candidiasis, cryptococcosis, aspergillosis, and mucormycosis (zygomycosis) |
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| What causes systemic candidiasis? |
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| candida albicans and other candida species |
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| What causes cryptococcosis? |
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| cryptococcus neoformans |
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| What causes aspergillosis? |
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| aspergillus fumigatus and other aspergillus species |
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| What causes mucormycosis (zygomycosis)? |
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| species of Rhizopus, Absidia, mucor, and other zygomycetes |
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| Where is tinea corporis usually located? |
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| nonhairy smooth skin |
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| What type of skin disease presents with circular pathces with advancing red, vesiculated border and central scaling with pruritis? |
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| tinea corporis (ring worm), most frequently caused by T rubrum and E floccosum |
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| Where is tinea pedis usually located? |
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| interdigital spaces on feet of person wearing shoes |
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| What are the acute and chronic presentations of tinea pedis? |
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| acute: itching, red vesicular chronic: itching, scaling, fissures |
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| What mycosis presents as pruritic, erythematous scaling lesion in intertriginous area? |
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| tinea cruris (usually caused by T rubrum, T mentagrophytes, E floccosum) |
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| What is endothrix versus ectothrix? |
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| endothrix is fungus inside the hair shaft ectothrix is fungus on the surface of the hair |
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| What does tinea capitis look like? |
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| circular bald pathces with short hair stubs or broken hair within hair follicles. Kerion rare. Microsporum-infected hairs flouresce |
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| What organisms cause tinea capitis? |
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| T mentagrophytes and M canis |
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| What organisms cause tinea barbae? |
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| T mentagrophytes |
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| What is tinea unguium? |
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| fungal infection of the nail in which nails are thickened or crumbling distally; discolored; lusterless. Usually associated with tinea pedis. Caused by T rubrum, T mentagrophytes and E floccosum |
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| What causes coccidioidomycosis? |
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| coccidiodes immitis |
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| Where in the environment and in what geographic locations do you get coccidioidomycosis from? |
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| soil semiarid regions of southwestern United States, Mexico, Central and South America |
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| What do the conidia of coccidioidomycosis look like? |
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| hyaline septate hyphae and arthroconidia, 3 X6 um |
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| What does the tissue form of coccidioidomycosis look like? |
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| spherules, 10-80 um or larger, containing endospores, 2-4 um |
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| What organism causes histoplasmosis? |
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| histoplasma capsulatum |
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| Where do you get histoplasmosis from (environment/geographically)? |
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| bat and avian habitats (guano); alkaline soil global: endemic in ohio, missouri,and mississippi river valleys; central africa (var duboisii |
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| What do the conidia of histoplasmosis look like? |
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| hyaline septate hyphae, tuberculate macroconidia, 8-16 um and small oval microconidia, 3-5 um |
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| What does the tissue form of histoplasmosis look like? |
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| oval yeasts, 2x4um, intracellular in macrophages |
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| What causes blastomycosis? |
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| blastomyces dermatidis |
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| Where do you get blastomycosis from in the environment? |
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| uknown (riverbanks?) endemic along missisippi, Ohio, and St. Lawrence river valleys and in southeastern united states |
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| What do the conidia of blastomycosis look like? |
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| hyaline septate hyphae and short conidiophores bearing single globose to piriform conidia, 2-10 um |
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| What does the tissue form of blastomycosis look like? |
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| thick-walled yeasts with broad-based usually single buds, 8-15 um |
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| What characterizes superficial mycoses? |
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| they colonize the keratinized outer layers of skin, hair, and nails. No immune system response so no damage (cosmetic only). Easy to diagnosis and treat |
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| What is the morphology of pityriasis (tinea) versicolor? |
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| clusters of round thick-walled yeast-like cells (3-8 um in diameter) mixed with short branced hyphae that orient end to end Appearance has been described as "spaghetti" (hyphae) and "meatballs" (yeast) |
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| T/F The organisms that cause Pityriasis versicolor (i.e. Melassezia) is considered "normal" flora. |
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| true! its not found as a saprophyte in nature or on animals so humans are the sole source of infection; considered "normal" flora |
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| How is Malassezia spread? |
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| through direct or indirect contact with infected keratinous flakes |
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| Why does Pityriasis Versicolor present as small hypo-pigmented or hyper pigmented macules? |
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| malassezia interferes with melanin production |
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| Where are Tinea versicolor lesions most often found? |
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| upper trunk, chest, shoulders, arms, neck and face |
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| T/F Pityriasis Versicolor never presents as pruitis. |
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| False, in severe cases there might be a mild pruitis |
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| What is the official name for dandruff? |
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| seborrheic dermatitis (possible caused by malassezia) |
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| How do you diagnose Pityriasis Versicolor? |
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| KOH prep on skin scrapings, lesions flouresce yellow under a Wood's lamp, organism can be cultured on mycologic agar supplemented with olive oil |
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| How do you treat pityriasis versicolor? |
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| topical or oral azoles or selenium sulfide |
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| What is the morphology of white piedra? |
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| mix of cell types (yeast, hyphae, pseudohyphae, and arthrospores) |
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| What are the clinical symptoms of white piedra? |
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| affects the hairs of the hot and moist groin and axillae, fungus surrounds hair shaft and forms a white to brown soft gooey swelling along the hair strand, the mass of fungi do not damage the hair shaft and can be easily removed by running a section of the hair between the thumb and forefinger |
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| How do you diagnose white piedra? |
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| microscopic examination of infected hair, inoculating Sabouraud's agar plate and seeing if dry, wrinkly, cream-colored colonies of Trichosporon will appear in 2 to 3 days |
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| How do you treat white piedra? |
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| topical azoles, shaving affected areas and imporving hygeine, and vinegar/water mixture (4:1) |
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| What's another name for cutaneous mycoses? |
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| dermatophytoses |
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| What class of fungi causes cutaneous mycoses? |
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| closely related group of keratinophilic and keratinolytic fungi that attack hair, skin and nails |
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| T/F Dermatophytoses are some of the most commonly seen infections but rarely life threatening. |
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| true |
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| Whata re the three taxonomically related genera of dermatophytes? |
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| trichophyton, epidermophyton, and microsporum |
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| Why are cutaneous infections limited only to upper most layers of the epidermis and penetration to granular layer is rare? |
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| because these fungi don't grow well at 37 C or in the prsence of serum |
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| What do most dermatophytoses manifast as in general? |
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| "ringworm" pattern with a ring of inflammatory scaling with diminishing inflammation towards the center |
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| What characterize the trichophyton species of dermatophytes? |
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| macroconidia are rare, but when present are cylindrical, smooth, and thin walled. Microconidia are numerous, spherical, teardrop, or peg-shaped. Hyphae might grow in a spiral fashion. Reverse of a T. Rubrum colony is red |
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| What are the different types of trichophyton species? |
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| rubrum, mentagorophytes, tonsurans and verrucosum |
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| What is the morphology of the dermatophyte, epidermophyton floccosum? |
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| macroconidia are smooth walled, borne in clusters of two or three and there are no microconidia produced |
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| What are some examples of microsporum species? |
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| canis, gypseum, and fulvum |
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| What is the morphology of microsporum species, a dermatophyte? |
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| numerous large, thick and rough walled macroconidia. Microconidia are rare |
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| Host susceptibility to dematophytes and cutaneous mycoses are influenced by what factors? |
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| moisture, heat, skin chemistry, exposure, youth and genetic predisposition |
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| What are the three classes of dermatophytes based on habitat? |
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| geophilic (soil), zoophilic (animals), anthropomorphic (humans, contagious) |
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| By what fungi particles are dermatophytes transmitted? |
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| arthrocononidia, hyphae, or keratinous material containing these elements (can remain viable for long periods of time) |
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| What are some clinical syndromes caused by cutaneous mycoses/dermatophytes? |
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| tinea corporis (ringworm), tinea pedis (athletes foot), and tinea cruris (jock itch) |
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| Tinea characterized by annular lesions with clearing scaly center surrounded by a red advancing border that is dry is called ___________. |
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| jock itch |
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| What is the most common of all dermatophytoses? |
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| tinea pedis |
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| Describe tinea infections (other than tinea pedis). |
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| annular lesions with clearing scaly center surrounded by a red advancing border that can be dry or vescular. Lesions expand centrifugally and are often pruitic (active hyphal growth is at the periphery of the lesion). These fungi are likely to spread from person to person |
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| What part of the hari does tinea capitis or tinea barbae infect? |
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| infection begins with hyphal invasion of the skin of the scalp with subsequent spread down the keratinized wall of the hair follicle, and infection of the hair begins just above the root, hyphae infect the non-living portion of the hair as it grows |
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| What does tinea capitis look like grossly? |
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| dull, gray circular patches of alopecia, scaling, and itching. Hairs are weakened and may break off easily near the scalp |
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| What are the different characteristics of endo thrix and ectothrix of tinea capitis? |
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| ectothrix is formed by hyphae of microsporum produce a chain of spores on the outside of the hair shaft as a sheat that flouresces green under a Wood's lamp endothrix is a hyphae of trichophyton that make spores within the hairshaft which do not flouresce |
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| How do you get a kerion from tinea capitis? |
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| infections with zoophilic fungi may induce severe inflammatory reactions called a kerion which resembles a pyodermic bacterial infection |
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| What do you call a dermatophyte infection of the nail? What organism commonly causes it? |
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| tinea unguium or onychomycosis T. Rubrum is the most common cause |
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| How do you diagnose infections of dermatophytes? |
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| KOH prep of skin scrapings and hair to look for diagnostic spores and hyphae. Microsporum-infected hairs flouresce yellow green under woods lamp. Innoculation of mycosel or Sabourad's agar to grow fungi (incubate plates 1-3 weeks at room temp. observe colonial morphology microscopic morphology) |
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| What are the treatments for dermatophyte infections? |
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| topical or oral azoles and terbinafine or removal of infected tissue (nail removal) |
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| The fungi causing subcutaneous mycoses live in... |
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| soil or on vegetation |
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| What is the morphology of sporotrichosis (sporothrix schenckii)? |
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| THERMALLY DIMORPHIC. at ambient temps its a mold (septate, hyaline hyphae and oval conidia borne on delicate sterigmata or in a flower petal configuration on conidiophores) at 35-37C, it is a small pleomorphic budding yeast (rarely seen histopathologically) |
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| T/F Lymphocutaneous Sporotrichosis (Sporothrix schenckii) grows rapidly. |
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| true |
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| What is the epidemiology of lymphocutaneous sporotrichosis? |
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| common in warm climates and endemic in Japan and North and South America. Associated with traumatic innoculation of soil, vegetation, or any organic matter contaminated with the fungus (occupational hazard ofr landscapers or gardeners). Zoonotic transmission reported in armadillo hunters in association with infected cats |
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| What are the clinical symptoms of infection with lymphocutaneous sporotrichosis? |
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| initial site of infection is usually an extremity (finger or toe) and lesion appears as a small nodule that might ulcerate. 2 weeks later, painless, secondary subcutaneous lymphatic nodules appear and follow the course of lymphatic drainage of initial lesion. Secondary nodules may ulcerate in time |
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| What is fixed sporotrichosis? |
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| occurs in Mexico as a single nonlymphantitic nodule that is limited and less progressive (high level of exposure and immunity in the endemic areas) |
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| How do you diagnose lymphocutaneous sporotrichosis? |
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| culture pus from ulcerated nodule or infected tissue. Mold grows as a yeast at 35C and as a mold at room temperature on most mycological agar. Can place mycelia growth at 35C and it will convert to yeast form |
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| What is the treatment for lymphocutaneous sporotrichosis? |
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| classic treatment is oral potassium iodide as a saturated solution in milk over 3-4 weeks drug of choice is oral itraconazole |
