Micro - Block 1

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Micro - Block 1
2013-03-02 13:50:28
Mycology Parasitology

Mycology and Parasitology
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  1. What are the 2 main differences between fungi and higher eukarytocis?
    Fungal membranes contain ergosterol instead of cholesterol.

    Fungi are surrounded by a rigid cell wall composed of carbohydrate polymers and protein
  2. What are the two morphologies of fungi?
    Yeast: unicellular, reproduce by budding or fission (3-15 um)

    Hyphae/Mycelium (mold): branching cylindric tubules varying in diameter (2-10 um)
  3. What are the 4 types of sexual spores?
    • Zygospores: large thick-walled, formed by fusion at tips of two sexually compatible gametangia
    • Ascospores: single-celled spores produced in an ascus, usually 4-8 per ascus.
    • Basidiospores: single-celled spores located on a club-shaped structure
    • Chyltridiomycetes: most primitive fungi, motile cells
    • Deutromycetes: do not produce any known sexual spores
  4. What are the 5 asexual reproductive elements?
    • Blastoconidia: budding
    • Chlamydoconidia: thick walled single cells that are resistant to adverse conditions¬†
    • Arthroconidia: single celled conidia formed by disjoining hyphal cells
    • Conidiospores: borne naked on specialized structures (macroconidia, microconidia)
    • Sporangiospores: single-celled, formed w/in sacs at the end of a special hyphae
  5. What are some diagnostic laboratory procedures to identify fungal infections?
    Direct microscopic examination (KOH technique, staining)

    Cultivation on blood agar, Sabouraud's agar - must include antibiotics to inhibit bacterial growth

    Serologic methods



    Mass spectrometry
  6. What are some good combination therapy techniques?
    • Inhibition of different stages of the same biochemical pathway (terbinafine and azoles)
    • Increased penetration of one agent into the cell through a permeabilizing activity of another agent (amphotericin b/flucytosine)
    • Inhibition of transport of one agent out of the cell by another agent (reserpine & azoles)
    • Simultaneous inhibition of different fungal cell targets (caspofungin with amp. B or azoles)
  7. Which combo therapy produces antagonistic effects?
    Azole depletes ergosterol which is a target for amphotericin B.
  8. Which fungi does not benefit from combo therapy?
  9. How does resistance develop to antifungal drugs?
    Fungi do not destroy or modify antifungal drugs.

    Resistance occurs through efflux pumps, target alterations, reduced access to drug targets.
  10. What is the eagle effect?
    Organism is resistant to high concentrations of the drug but susceptible to low concentrations.
  11. Malassezia furfur:
    Infection site
    Additional information
    • Yeast (infrequent branched hyphae)
    • Skin (pink to brown)
    • Pityriasis (tinea) versicolor
    • Wood's lamp yellowish - spaghetti&meatballs
    • Local: azoles/selenium sulfide
    • Widespread: oral azoles
  12. Hortaea weneckii/Expophilia werneckii
    Clinical Syndromes
    Lab Diagnosis
    • Tinea nigra
    • dermaticeaous (dark colored) frequently branched, septate hyphae
    • black mold with annelloconidia¬†
    • tropical/subtropical regions - africa, asia, s. america
    • contracted by inocculation into superficial layers of epidermis
    • solitary, irregular, pigmented macule, usually on palms or soles - can resemble malignant melanoma
    • infection not contagious
    • direct microscopic visualization of fungal elements in KOH prep
    • azoles/terbinafine
  13. Piedraia hortae
    • Black piedra
    • Brown-reddish-black mold w/ ascospores on cultures
    • Latin america/central africa - poor hygiene
    • Hard dark nodules surround hair shaft
    • Tx: haircut, washing, topical antifungals
  14. Trichosporon inkin, asahii, mucoides
    • White piedra
    • Yeast-like
    • Hyphal elements, arachronidia, blastoconidia
    • Tropical/subtropical regions - poor hygiene
    • Surrounds hair shaft and forms white-brown swelling- groin axillae
    • Microscopic exam, culture w/o cyclohexamide - cream colored dry
    • Tx: remove hair, improve hygiene, topical azoles
  15. What are the 3 dermatophytes and their morphology?
    • trichophyton: numerous, spherical or teardrop/peg shaped micronidia - rare, smooth-thin walled macronidia
    • epidermophyton: smooth walled, clusters of 2-3 macronidia, absent micronidia
    • microsporum: numerous, large, thick, and rough walled macronidia, rare micronidia
  16. What is the morphology of dermatophytes?
    hyaline septate hyphae, chains of arthroconidia and dissociated arthroconidia - restricted to nonviable skin b/c unable to grow at 37degrees or serum
  17. What are the ecological categories of dermatophytes and how do they respond to therapy?
    Zoophilic/geophilic: elicit strong host response and respond well to therapy

    Antrophilic: chronic infection, mild host response, difficult to cure
  18. What 2 fungi account for 80-90% of all dermatophytic infections?
    Trichophyton rubrum & mentagrophytes
  19. Sporothrix schnecki
    • subcutaneous mycoses
    • lymphocuteanous sportrichosis
    • traumatic induction through dermis
    • soil & decaying matter
    • thermally dimorphic
    • warmer climates: Japan and Americas
    • inoculation site is nonpainful - appears as nodular lesion that will ulcerate - series of linearl nodules can appear as it spreads through lymphatics

    culture = definite dx

    • Tx: oral KI in developing countries (adverse SE)
    • itraconazole: safe effective, adminster 3-6 mos.