-- MEDICAL VIROLOGY & MYCOLOGY MOUNT KENYA UNIVERSITY — MBCHB YEAR 3 UNIT CODE: MBMM 3300 / MBMM 3333 TARGETED EXAM NOTES — SECTION 2 OF 3 --- MYCOLOGY FUNDAMEN
-- MEDICAL VIROLOGY & MYCOLOGY MOUNT KENYA UNIVERSITY — MBCHB YEAR 3 UNIT CODE: MBMM 3300 / MBMM 3333 TARGETED EXAM NOTES — SECTION 2 OF 3 --- MYCOLOGY FUNDAMENTALS General characteristics of fungi - Eukaryotes - Heterotrophic organisms - Cell walls made of chitin - Can be unicellular or multicellular - Exist as yeasts, molds, or mushrooms - Reproduce by both sexual and asexual spores - NOT photosynthetic — this is the false statement MCQ trick Hyphae and mycelium - Hyphae are filamentous structures making up the mycelium - A fungal mycelium may contain: septate hyphae, coenocytic cytoplasm, chitinous cell walls, mitochondria — all of the above - Separating wall in hyphae is called a septum, not hyphae — MCQ trick - Cell wall contains chitin — a polysaccharide Cell membrane - Major component of fungal cell membrane: ergosterol - NOT cholesterol, NOT peptidoglycan — these are trick options - Ergosterol is the target of most antifungal drugs pH for fungal growth - Best growth range: pH 4-6 Staining - Fungal cell wall with periodic acid Schiff stain: appears red --- FUNGAL CLASSIFICATION Classes based on reproduction - Zygomycota: sexual reproduction by zygospores - Ascomycota: sexual reproduction by ascospores - Basidiomycota: sexual reproduction by basidiospores - Chytridiomycota: sexual reproduction by zoospores - Mitosporic fungi / Deuteromycetes / Fungi Imperfecti: NO known sexual stage Deuteromycetes — Fungi Imperfecti - Sexual reproduction method not clearly known - They are imperfect fungi - Also called Deuteromycetes - Answer is B and C together Dimorphic fungi - Exist as mold at environmental temperature and yeast at body temperature - Most dimorphic pathogens are filamentous at 23°C and yeast at 37°C - Examples: Histoplasma, Blastomyces, Coccidioides, Paracoccidioides, Sporothrix --- FUNGAL REPRODUCTION Asexual spore formation - Arthrospores: single celled spores from fragments of hyphae - Conidia: asexual spores - Sporangiospores: asexual spores - Yeast budding: asexual - Basidiospores are NOT asexual — they are sexual, found in club-shaped structure called basidium Sexual spores - Ascospores: produced in a sac - Basidiospores: single celled, found in club-shaped structure - Zygospores: Zygomycota Asexual methods in fungi - Fragmentation, budding, fission - NOT spermatization — that is sexual --- ANTIFUNGAL DRUGS Essay and MCQ — modes of action heavily tested. Polyenes - Nystatin and Amphotericin B - Target: ergosterol in cell membrane, disrupts membrane integrity - Nystatin belongs to polyene class - Amphotericin B: broad spectrum, used for blastomycosis, histoplasmosis, aspergillosis, valley fever - NOT used for ergotism Azoles - Fluconazole, Miconazole, Ketoconazole, Itraconazole, Voriconazole, Posaconazole - Target: ergosterol biosynthesis — inhibit proper formation of plasma membrane - Miconazole inhibits plasma membrane formation - Fluconazole: drug of choice for most candida infections - Posaconazole: alternative for fluconazole-resistant Candida glabrata - Itraconazole: drug of choice for sporotrichosis Echinocandins - Micafungin, Caspofungin - Target: glucan synthesis in cell wall — NOT ergosterol - Antifungal drug class that targets glucans Allylamines - Terbinafine - Target: ergosterol biosynthesis Griseofulvin - Target: DNA — inhibits microtubule formation, disrupts mitosis Flucytosine - Target: DNA synthesis - NOT a microtubule — trick MCQ option 5-Flucytosine and Fluconazole similarity - Both are antifungals used for systemic infections Drug that does NOT target ergosterol biosynthesis - Micafungin — targets cell wall glucans --- SUPERFICIAL MYCOSES These affect only the outermost layers of skin and hair. No inflammation. Tinea nigra - Caused by Hortaea werneckii - Pigmented macules on palm and soles - Non-inflammatory, non-scaly - NOT difficult to isolate by microscopy — trick false statement - Usually related to poor hygiene White piedra - Caused by Trichosporon species - Superficial infection of hair - Species causing scalp hair white piedra: Trichosporon ovoides — repeated MCQ - Other species: T. inkin, T. asahii, T. mucoides Black piedra - Caused by Piedraia hortae - Hard black nodules on hair Tinea versicolor / Pityriasis versicolor - Caused by Malassezia furfur - Lesion characteristics: hypopigmented and hyperpigmented irregular macules on the skin - NOT round and smooth — that is the trick option - Mild itching, scaling, non-contagious - Appears on back, chest, upper arms, underarms - Least frequently associated with immunocompromised persons Superficial mycoses list - Tinea nigra, Tinea versicolor, White piedra, Black piedra - Tinea imbricate is NOT superficial — it is cutaneous --- CUTANEOUS MYCOSES — DERMATOPHYTOSES Essay question in multiple papers — high priority. General characteristics - Affect hair, skin, and nails — keratinized tissues - Caused by dermatophytes: Trichophyton, Microsporum, Epidermophyton - Commonly called ringworm or tinea Three genera of dermatophytes - Trichophyton: infects hair, skin, nails — has microconidia - Microsporum: infects hair and skin — has macroconidia - Epidermophyton: infects skin and nails — does NOT have microconidia Zoophilic vs anthropophilic - Acute infections: associated with zoophilic dermatophytes such as Microsporum canis - Chronic infections: associated with anthropophilic dermatophytes - Zoophilic dermatophytes: Microsporum canis, Trichophyton equinum, Trichophyton simii, Microsporum nanum — all of these Types of tinea - Tinea pedis: athlete's foot — between toe webs and soles - Tinea corporis: ringworm of body - Tinea capitis: scalp ringworm - Tinea unguium: nail infection — onychomycosis - Tinea cruris: jock itch — groin - Tinea versicolor: caused by Malassezia, not a dermatophyte Tinea pedis — athlete's foot - Itchy, white flaky, stingy patches between toe webs and soles - Characterized by inflammation and skin fissures - Etiological agent: Trichophyton rubrum - Common cause of athlete's foot: wearing tight shoes, sweating, keeping feet wet — all of the above Tinea capitis — scalp ringworm - In 2-year-old child with rash from pet cat: Microsporum canis - Microsporum canis is zoophilic — transmitted from animals Laboratory diagnosis of dermatophytes - Most reliable method for Trichophyton rubrum: skin scrapings with KOH microscopy - Circular dry scaly pruritic lesion with branching septate nonpigmented hyphae in KOH preparation: Dermatophytosis - Epidermophyton and Microsporum: both cause cutaneous mycoses, both have macroconidia Nail infections — onychomycosis - Caused by: Epidermophyton floccosum, Trichophyton rubrum, Trichophyton mentagrophytes - NOT caused by: Microsporum canis — trick answer --- SUBCUTANEOUS MYCOSES These involve the deeper dermis and subcutaneous tissue, usually after traumatic inoculation. Sporotrichosis - Caused by Sporothrix schenckii — dimorphic fungus - Classic scenario: girl pricks finger on rose bush, develops pustule progressing to ulcer, nodules along lymphatic drainage - Ecology well known — lives in soil and decaying vegetation - Most cases involve lymphangitic spread - Drug of choice: itraconazole - NOT most patients immunocompromised Chromoblastomycosis / Chromomycosis - West African farmer with persistent scaly papule progressing to cauliflower-like lesions - In tissue: organisms convert to spherical cells reproducing by fission with transverse septations - Etiologic agents are environmental, NOT endogenous mammalian flora - Caused by multiple species, NOT single species - Most infections are subcutaneous, NOT systemic - Production of sclerotic bodies: Phialophora verrucosa Phaeohyphomycosis - Brain abscess with darkly pigmented septate hyphae: caused by Cladophialophora species - May show subcutaneous or systemic disease including sinusitis - Responds to itraconazole Mycetoma - Essay question — appears in multiple papers - Two types: - Eumycetoma: caused by true fungi e.g. Madurella mycetomatis - Actinomycetoma: caused by bact