General Mycology Lecture Notes PDF

Level (1) - Semester (1) MICROBIOLOGY D R Z I A D M A LECTURE (8) H A N GENERAL MYCOLOGY A -  Mycology is study of fungi.  Natural habitats of almost all fungi are soil & water.  Eukaryotic organisms: having true nucleus, nuclear membrane.  Rigid cell wall:...

Level (1) - Semester (1) MICROBIOLOGY D R Z I A D M A LECTURE (8) H A N GENERAL MYCOLOGY A -  Mycology is study of fungi.  Natural habitats of almost all fungi are soil & water.  Eukaryotic organisms: having true nucleus, nuclear membrane.  Rigid cell wall: of chitin, glucans, mannans & complex polysaccharide (Bacteria???).  Cell membrane: contains ergosterol.  Obligate aerobes/Facultative anaerobes.  Grow within a wide temperature & PH range. ① Yeast & Yeast Like Fungi ② Filamentous Fungi ③ Dimorphic Fungi  - Round to oval unicellular fungi. Round to oval multi-cellular fungi. Reproduce by budding or fission. Reproduce by budding. Progenitor then detached from mother Buds fail to detach giving a pseudohyphae. cell. Ex. Cryptococcus neoformans. Ex. Candida.  Filamentous fungi tubular, branched, septated or aseptated hyphae.  The hyphae when branch form "mycelium'  Vegetative hyphae: part of hyphae anchor the colony, absorb nutrients.  Aerial hyphae: part project above reproductive structure.  Aspergillus.  - Parasitic phase Saprophytic phase Occurs in host tissue & Occurs in soil & On enriched media On ordinary media At 37°C. At 22-25°C. Offspring arise from single parent, Offspring arise by Meiosis. Only by mitosis.  Sporangiospores: endogenous spores in  Ascospores: Spores form within a sac sporangium. (ascus).  Conidiospores: exogenous spores;  Basidiospores: Spores form on a arthrospores. basidium. -  Toxin production.  Physiologic alteration: fungi increase metabolic activity to invade tissue.  Capsule.  Enzyme production: phospholipases.  Thermotolerance:  Melanin production: protects fungi from phagocytosis, temp. extremes & UV.  Biofilm formation. ① Hypersensitivity due to environmental exposure to fungal spores. ② Infection (Mycosis) due to invasion of tissue & organs. ③ Toxicosis: 2 types a) Mycotoxicosis due to accidental consumption of food contaminated by fungal toxin; Aflatoxicosis due to consumption of grain infected with Aspergillus flavus; hepatic cell carcinoma. b) Mycetismus: due to ingestion of Mushroom with preformed toxin. -  Infection is restricted to outermost layers of:  Skin & hair, T. versicolor.  Fungi invade deeper into:  Epidermis, hair & nail but  NOT dermis; Dermatophytes.  Infection involving:  Dermis,  Subcutaneous tissue,  Muscle  Fascia mycetoma.  Fungal infection by:  fungal flora (Candida) or  fungi in the environment (Aspergillus).  Infections occur in immunocompromised patients:  Diabetic  Cancers  Corticosteroid  Immunosuppressive (Cytotoxic drugs) treatment.  Multi organs (primarily lung) affection by dimorphic fungi.  Due to inhalation of fungal spores or spread of local mycosis.  Histoplasmosis.  -  Specimens:  Differ according to site of infection.  2 parts: ① One for microscopy ② Other for culture.  Examination:  KOH 10-20%,  Dissolve keratin  Gentle heating,  Cellular material.  Lectophenol cotton blue,  Indian ink.  Gram stain,  Tissue biopsy,  Gomori methenamin silver. -  Sabouraud dextrose agar "SDA" +chloramphenicol + cycloheximide: prevent bacterial & saprophytic fungal contamination.  2 cultures are incubated at 25°C & 37°C to reveal dimorphism, for at least 3 wks.  Macroscopic appearance.  Microscopic.  Nucleic Acis Probe.  ID tests.  ELISA. -  Fungal cells (as human cells) are eukaryotic.  Most of substances that kill or inhibit fungi are also toxic to host cell. ① Cell wall synthesis inhibition:  Echinocandins: Caspofungin, inhibits glucan synthesis. ② Ergosterol synthesis inhibition:  Azoles: Fluconazole (BBB), Voriconazole. ③ Cytoplasmic membrane function alteration:  Polyenes: Amphotericin B & its lipid preparation (liposomal amphotericin-B). ④ Nucleic acid synthesis inhibition:  Fluocytosine.  Group of mycoses caused by commensal & saprophytic fungi in immuno-compromised individuals. ① Cryptococcosis. ② Candidiasis. ③ Aspergillosis.  -  Major problem occurs after antibiotic &  Diseases caused by a number of  Capsulated yeast corticosteroid therapy. Aspergillus species. cryptococcus  Candida is present as normal flora  Their spores are common in neoformans often found (intestinal, oral cavity, vagina). environment; soil, food. in pigeon droppings.  C. albicans is responsible for most of  A. fumigatus is the main human infections. opportunistic pathogen. ① Superficial lesion. ① Superficial Aspergillosis: in a) Mucous membrane: paranasal sinuses, external ear,  Oral thrush: discrete white patches or eye. on tongue & buccal mucosa. ② Respiratory disease:  Vaginal thrush: white lesion on a) Bronchial asthma: following vulva, vagina & cervix. inhalation of spores. b) Skin: Infection occurs in moist warm b) Aspergilloma: fungus ball area as axilla, groin & submammary occurs on preexisting lung ① Lung infection. fold. cavity (TB). ② Cryptococcal meningitis c) Nail: Infection of nail fold. ② Invasive Aspergillosis: (HIV Patients). ③ Systemic lesion: heart, lung, kidney. Hematogenous spread of fungus to organs.  - ① Specimen: According to site of infection. ① Specimen: according to site of ② Examination: infection. a) Direct microscopy: KOH, Lactophenol ② Examination:  India ink (capsulated blue or Gram-stained smear (Gram a) Direct microscopy: KOH yeast cell in CSF). +ve), budding yeast with mount & Lactophenol blue:  Creamy, white colonies pseudohyphae septated dichotomous on SDA after 1-2 days. b) Culture: On SDA, white, creamy, branching hyphae (one stem smooth colonies with yeast odor. gives raise to two branches. ③ Identification of C. albicans: Germ tube These two branches give formation: Filamentous outgrowth when raise to two each and so on. grown on human serum at 37°C for b) Culture on SDA; A. 3hours (formation of germ tube). fumigatus: greenish.  - Clinical Case  A 49-year-old patient with rheumatoid arthritis comes into the clinic with a fever. Patient's current medications corticosteroids. He has fatigue, chest pain, cough and hemoptysis. He works as a grain a grain inspector at a large farm cooperative. Sputum culture recovered green colonies which under microscope showed dichotomous branched hyphae. ① Fungal cell wall is formed of: a. Peptidoglycan. b. Mannan. c. Phospholipids. d. Ergosterols. ② Asexual fungal spores include: a. Ascospores. b. Endospores. c. Basidiospores. d. Arthrospores. ③ List 4 mechanisms of antifungals. ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..…………..