Fungi: Cell Structure & Classification PDF

Fungi: Cell Structure & Classification Assist. Prof. Dr. GÜNER EKİZ NEU Faculty of Pharmacy Department of Pharmaceutical Microbiology 31.10.2023 1 2 Bacteria vs Fungi 3 Mycology ≥150 000 species! Only about 300 species of fungi cau...

Fungi: Cell Structure & Classification Assist. Prof. Dr. GÜNER EKİZ NEU Faculty of Pharmacy Department of Pharmaceutical Microbiology 31.10.2023 1 2 Bacteria vs Fungi 3 Mycology ≥150 000 species! Only about 300 species of fungi cause human diseases They grow in nature as saprophytes on dead organic material, and they are important catalysts in the carbon cycle. Producers of drugs (antibiotic – penicillin; immunosuppressant – cyclosporin,…) Food microbiology & Industrial microbiology Eukaryotic 4  Pathogenic species! Plant pathogens Animal pathogens Human pathogens 5  Human Pathogens (1) It must be able to grow at a high temperature, at or above 37°C. (2) ) It must be able to reach the tissues it will parasitize, by penetrating host tissue barriers, or by circumventing them through small airborne cells that enter air-filled spaces of lungs and sinuses directly. (3) It must be able to digest and absorb components of human tissues. (4) It must be able to withstand the human immune system. 6 General Characteristics Fungi lack chlorophyll and do not engage in photosynthesis (different from plants) They produce spore structures (sexual-asexual spores) Fungal spores are microscopic biological particles that allow fungi to be reproduced Spore morphology is one of the most important features used for visual identification of fungi 7 General Characteristics 8  Fungal Cell Wall Cell Wall: Complex and rigid cell wall composed of mannoproteins, chitins, α- and β- linked glucans (90%) lipids, protein (% 10) 9 Structural organization of the cell walls of fungal pathogens 10 11 Fungal Cell Membrane ERGOSTEROL is a specific target for antifungal agents Cell membrane: The membrane is bilayered with inclusion of sterol (ergosterol, zymosterol), in contrast to the cholesterol typically found in higher eukaryotic membranes. 12  Capsule Cryptococcus neoformans Complex polysaccarides Main virulence factor In the environment, the capsule plays a role in the protection of the organism against some stress conditions ü Disease caused by Cryptococcus species = Cryptococcosis 13 Growth Conditions Optimum growth temperature: 20-350C Most fungi require a humidity level over 75% to grow pH 5 – 7 (generally like acidic pH levels) aerobic or facultative anaerobic Chemoheterotrophs Growth rate: 1 - 2 days for Yeasts 4 - 21 days for Molds 14 Nutrition & Physiology Feed by secreting extracellular enzymes that digest polymeric materials (e.g. polysaccharides or proteins) into monomers that are assimilated as sources of carbon and energy Decomposers (digest dead animal and plant materials) Inorganic substances and salts Fungi tend to be more resistant to environmental stress conditions than bacteria! 15 Fungi Groups: On the Basis of Morphology Yeasts: Unicellular Molds: Multicellular (filamentous fungi) Dimorphic fungi: § Ability to exist in two forms: i. Yeast phase at 35- 37°C ii. Mold phase at 25°C This is usually brought about by change in temperature and the fungi are also described as thermally dimorphic fungi. Talaromyces marneffei, a human pathogen that grows as a mold at room temperature, and as a yeast at human body temperature. 16 Dimorphism of Candida albicans DYC : Daughter Yeast Cell GT : germ tube H : Hyphae YMC : Yeast Mother Cell Ph : Pseudohyphae 17 Fungi: Molds & Yeasts Molds (Filamentous Fungi) - Yeasts 18 Yeasts Unicellular - spherical, oval - 3 - 15 μm Reproduce by budding - Pseudohyphae: a chain of elongated budding cells that have failed to detach (not true hyphae) Form a bacteria-like colony (creamy) 19 Yeasts (budding and pseudohyphae) 20  Molds (Filamentous Fungi) Multicellular, forming a network of filaments called hyphae (singular, hypha) 2 -10 μm Septate- coenocytic (aseptate hyphae)– Identification! Woolly (Fuzzy) appearance in culture The hyphae form together to produce a mat- like structure called a mycelium 21 Types of Hyphae Vegetative hyphae: penetrate the media and absorb food Aerial hyphae : are directed above the surface of media Reproductive hyphae: Aerial hyphae that carry different spores Mycelium: A collection of hyphae 22 Hyphal growth from spore 23  Reproduction Fungi reproduce sexually and/or asexually. Perfect fungi reproduce both sexually and asexually, while imperfect fungi reproduce only asexually (by mitosis) In both sexual and asexual reproduction, fungi produce spores that disperse from the parent organism Asexual reproduction: through the formation of asexual spores, which are produced by one parent only (through mitosis) Sexual reproduction: Sexual reproduction is carried out by diffusion of compatible nuclei from two parent at a definite state in the life cycle of fungi (plasmogamy, karyogamy, meiosis) 24 Reproduction 25 Reproduction - Anamorph: asexual reproductive stage - Teleomorph: Sexual reproductive stage Asexual form of molds (anamorph) and the sexual form of molds (teleomorph) have diferent morphologies and have historically had diferent names. Histoplasma capsulatum – Ajellomyces capsulatum 26 Types of Fungal Spores asexual sexual 1. Arthrospore 1. Ascospore 2. Blastospore 2. Basidiospore 3. Chlamydospore 3. Oospore 4. Conidiospore 4. Zygospore Microconidium Macroconidium 5. Sporangiospore 27 Types of asexual spores 28 Arthrospore Oval/cylindrical spores are formed by breaking up of fungal mycelium A spore is formed by separation followed by fragmentation of hyphae Examples: Trichosporium, Geotrichum, Coccididious imitis 29 Blastospore Budding spores usually formed at the terminal end of hyphae These spores may remains attached to the hyphae (branching chain of blastospores) Pseudohyphae- Candida albicans Examples: Ascomycetes, Basidiomycetes, Zygomycetes 30 Chlamydospore Usually formed during unfavourable condition Thick-walled spores: highly resistant to adverse condition When favourable condition returns, each chlamydospore give rise to a new individual fungi Examples: Ascomycetes, Basidiomycetes, Zygomycetes 31 Conidiospore Asexual spores that form on the tip or side of aerial hyphae, called conidiophore Examples (Aspergillus, Penicillium) 32 Dermatophytes (Microsporum, Trichopyton) Microconidia Unicellular Macrocinidia Multicellular 33 Dermatophytes 34 Sporangiospores Asexual spore are produced in a sac like structure called sporangia (singular: sporangium) Sporangium are produced at the end of special aerial hyphae called sporangiophore Sporangium contains large numbers of haploid spores, which are released by rapture of sporangial wall Example: Rhizopus 35 36 Sexual Reproduction The process of sexual reproduction involves three phases: 1) Plasmogamy: fusion of protoplasm 2) Karyogamy: fusion of nucleus 3) Meiosis: reductional nuclear divions 37 Ascospore Ascospores are the characteristic spores of the largest group of fungi, the Ascomycota or ascomycetes. Usually single-celled, produced in a sac called ascus (plural;asci) and usually there are 4-8 ascospores in an ascus but the number may vary from species to species Ascospores are usually arranged in a linear order 38 Basidiospore Basidiospores are the sexual spores which characterize a large group of fungi, the Basidiomycota or basidiomycetes. Spores are formed in a club shaped structure, called basidium 39  Zygospore Zygospores are typical of Zygomycota Thick-walled spores “sexually produced resting structures” formed when two sexually compatible hyphae or gametangia of certain fungi fuse together Zygospore germination may be by a germ tube or by the formation of a germ sporangium. 40 Oospore Sexually produced spores of Oomycota Formed within a special female structure: Oogonium Male gamete: Antheridium 41 Fungi Classification: Based on Sexual Reproduction Ascomycota Basidiomycota Zygomycota Deuteromycota – Fungi Imperfecti Sexual state not present or not discovered No longer formally accepted as a taxon, many of the fungi it included have yet to find a place in modern fungal classification. Examples: Candida albicans, Coccidioides immitis 42 43 Opportunistic pathogens Microorganisms Do not cause disease in a healthy host Take advantage of a host with a weakened immune system E.g. some bacteria, viruses, fungi and protozoa 44 What are the opportunities? Physiological factors e.g. elderly, pregnancy and infancy Local factors e.g. mucosal irritations, poor dental hygiene, localized radiotherapy, xerostomia Medications e.g. broad spectrum antimicrobial therapy, cytotoxic drugs, immunosuppressive drugs, Steroid inhalers and systemic steroids Nutritional factors e.g. Iron, folate, vitamin B12 deficiencies, malnutrition Systemic disorders e.g. Diabetes, hypothyroidism, Addison’s disease Immune defects e.g. HIV infection, AIDS, thymic aplasia Malignancies e.g. acute leukaemia, agranulocytosis Xerostomia due to irradiation, Sjogren's syndrome, drug therapy 45  Fungal Infections (Mycoses) Superficial – Hair – Skin Cutaneous – Keratinized tissue Subcutaneous Systemic Opportunistic 46 Mycoses Superficial Mycoses: superficial infections of skin and hair Cutaneous Mycoses: infections of keratinized tissue-skin, hair, nails-caused by dermatophytes Subcutaneous Mycoses: usually introduced by trauma/breach of dermal tissue - infections of subcutaneous fascia, muscle and deeper epidermal layers Systemic mycoses due to primary pathogens (systemic dimorphic fungi) The primary deep pathogens usually gain access to the host via the respiratory tract. Systemic mycoses due to opportunistic pathogens Opportunistic fungi causing deep mycosis invade via the respiratory tract, alimentary tract, or intravascular devices. All three (superficial, subcutaneous, and cutaneous mycoses) are typically noninvasive infections. Systemic mycoses, on the other hand, can be life threatening, especially when the host is immunocompromised. 47 48 Targets of some antifungal agents 49