Biology of Fungi Updated Lecture..pdf

Learning Objectives • Know basic characteristic of fungi. Biology of Fungi Dr. Hasan Alfahemi • Know the classification of true versus pathogenic fungi. • - Know beneficial and harmful effects of fungi • - Describe fungal reproduction methods. • - Discuss the fungal pathogenicity and predisposing...

Learning Objectives • Know basic characteristic of fungi. Biology of Fungi Dr. Hasan Alfahemi • Know the classification of true versus pathogenic fungi. • - Know beneficial and harmful effects of fungi • - Describe fungal reproduction methods. • - Discuss the fungal pathogenicity and predisposing factors for fungal infection. • - Know the main laboratory diagnosis tests for fungal infection. What are Fungi • They are diverse group of saprophyte (derives nourishment from dead organic matter). • Parasitic eukaryotic organisms. • Formerly considered to be plants, now generally assigned their own kingdom, Mycota. • Virtually all organisms are subject to fungal infections. • There are around 100000 fungal species, only about 100 have pathogenic potential for humans. • Most human fungal infections are nosocomial and/or occur in immunocompromised individuals (opportunistic infections). Source: Lippincott’s Illustrated Review, Microbiology, 2nd Edition. How do fungi differ from other microbes? • Fungi can be distingushed from other infectious microorganisms, bacteria and viruses, as they are eukaryotes. • Their cell wall and cell membrane are fundamentally different from those of bacteria and other eukaryotes. Characteristic of fungi 1).Vegetative Hypha: Composed of cells involved in catabolism and growth. • Fungal cell wall is mainly composed of Chitin. • Chitin is a polymer N-acetylglucosamine rather than peptidoglycan. • Therefore, fungi are not affected by antibiotics (Penicillin). • Fungal cell membrane composed of ergosterol rather than cholestrol found in mammalian membranes. • Antifungals are mainly targeting parts of these cellualar components and inhibiting its biosynthesis. E.g. (amphotericin B, Nystatin, and imidazole antifungal drugs). 2).Reproductive Hypha (aerial) Composed of cells involved in reproduction (produce spores). Both sexual and asexual spore may be produced Store their food as glycogen 31/3/16 1. Yeast : unicellular, 370C (Non-filamentous) Molds – Budding Yeast uneven reproduction– pseudohypa – Fission yeast-even reproduction 2. Mold :Filamentous, multicellular, hyphae, 250C 3. Dimorphic fungi (thermally dimorphic fungi) : mold yeast phase. phase & Note: Some fungal species especially those of systemic mycosis are dimorphic, being usually yeast-like in one environment and mold-like in another, being affected by temperature and carbon dioxide. 31/3/16 YEAST MOULD • Unicellular • Multicellular • Micro.:Oval to round (Dia: 3-15 µm) Macro.: Pasty colonies (resemble bacteria) • Micro.: Hypha(e) (dia: 2-10 µ • • m)Spores / conidia. •Macro.: Surface texture: Cottony/ powdery/ wooly/velvety/granular • /glabrous Yeast Fungal Taxonomical Classification Four groups of true fungi 1-3 reproduce sexually 1).Zygomycetes (bread mold—Rhizopus) zygospore- sexual spore class Basidiomycetes 2). (puffballs & mushrooms) Basidiospore- sexual spore class Ascomycetes 3). Ascospore- sexual spore class Deuteromycetes (fungi imperfection) 4). have NO sexual reproduction Benefecial Effects of Fungi Harmful Effects of Fungi 1. Decomposition. 2. Sources of antibiotics, ex:Penicillin. 3. Some fungi are edible (mushrooms). 4. Supplements - vitamins and cofactors. E.g. (Coenzyme Q (ubiquinone or CoQ) is an essential lipid 1.Destruction of food, lumber, paper, and cloth. 2. Diseases, including allergies. 3.Toxins produced by poisonous mushrooms and within food (Mycetism and Mycotoxicosis). 4. Plant diseases. 5. Spoilage of agriculture produce. 6.Damage the products such as magnetic tapes and disks, glass lenses, marble statues, bones and wax. that plays a role in mitochondrial respiratory electron transport and serves as an important antioxidant. In human and yeast cells, CoQ synthesis derives from aromatic ring precursors and the isoprene biosynthetic pathway). 5. Penicillium is used to flavour cheeses. 6. Ergot -alkaloids àthat help in inducing uterine contractions, controlling bleeding and treating migraine. Potent alpha blocker. 7. Fungi -trap mosquito larvae-Malaria control. Sexual spore • Fungal reproduce by : 1. 2. 3. 4. – Asexual – Sexual – Parasexual –gene exchange Zygospore Ascospore Basidiospore Oospore • Asexual – Hyphae fragmentation – Asexual spores • • • • Conidiosphore-Asperigillus Arthroconidia- Coccidioido immitis Blastoconidia- Candida albicans sporangiospore- Rhizopus • Have three stages: – Plasmogamy- a haploid nucleus of donor cells – Karyogamy- the (+) and (-) nuclei fuse to form a diploid zygote – Meiosis – the diploid nucleus give rise to haploid nuclei (sexual spores) genetic recombinant . Mycoses-Pathogenesis Most fungi are saprophytic or parasitic. Risk factors: Conditions are favourable. True pathogens: dimorphic fungi -systemic mycoses and dermatophytes, which are primary pathogens, the rest are only opportunistic. Ex: Candida and Malasezzia have adapted to human environment and exist as commensals. The complex interplay between fungal virulence factors and host defence factors will determine if a fungal infection will cause a disease. Infection depends on inoculum size and the general immunity of the host. Source: Lippincott’s Illustrated Review, Microbiology, 2nd Edition. Fungal Pathogenicity • Ability to adhere to host cells. • Production capsules allowing them to resist phagocytosis •Production of a cytokine -suppress the production of complement. Ability to acquire iron from red blood cells as in Candida albicans • Ability to damage host by secreting enzymes such as keratinase e, elastase, collagenase • Ability to resist killing by phagocytes as in dimorphic fungi • Ability to secrete mycotoxins • Exhibiting thermal dimorphism • Ability to block the cell-mediated immune defences of the host. • Surface hydrophobicity. Laboratory Diagnosis of Mycoses • • • • • • • • Direct microscopic examination KOH mount Calcofluor white India ink Culture SDA,PDA, Corn Starch Agars The tease mount Scotch tape preparation • The microslide culture technique( slide culture) • Serology • Molecular techniques: DNA hybridization, PCR #HariPanVan@Asst Prof@BMC 31/3/16 Factors predisposing to fungal infections • Prolonged antibiotic therapy • Underlying disease (HIV infection,cancer, diabetes,) • Age • Surgical procedures • Immunosuppressive drugs • Irradiation therapy • Indwelling catheters • Obesity • Drug addiction • Transplants • Occupation • Poor hyiegene Initial observations in the study of fungus isolates 1.Appearance of the growthSubverse/reverse 2. Rate of growth (3-5d),(10d),and (14d) 3. Colony pigmentation 4.Growth on media containing antifungal agents 5.Dimorphic fungi (22-25 OC) & (30-35 OC) Reference Harvey RA et al. Lippincott’s Illustrated Reviews: Microbiology Third Edition, 2013, Chapter 20, Page 203-206