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Introduction to Mycology

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1 Introduction to Mycology
Over the course of time, more than 100,000 species of fungi have been recognized and described. However, fewer than 500 of these species have been associated with human disease. The remainders are only able to produce disease in hosts that are debilitated or immunocompromised.

2 What is mycology? Mycology is the study of fungi. The disease caused by fungi is called MYCOSES. What are fungi? Eukaryotic, spore-bearing, heterotrophic that produce extracellular enzymes and absorb their nutrition.

3 General information's about FUNGI:
Fungi are not plants or animals, they form a separate group of higher organisms, distinct from both plants and animals, which differ from other groups of organisms in several major respects: First: Fungal cells are encased within a rigid cell wall, mostly composed of chitin and glucan. These features contrast with animals, which have no cell walls, and plants, which have cellulose as the major cell wall component.

4 Second: Fungi are heterotrophic. This means that they are lacking in chlorophyll and cannot make their organic food as plants can, through photosynthesis. Fungi live embedded in a food source or medium, and obtain their nourishment by secreting enzymes for external digestion and by absorbing the nutrients that are released from the medium. Some live on humans e.g. the cause ringworm infections. Some live on insects, or plants. Third: Fungi are simpler in structure than plants or animals. There is no division of cells into organs or tissues.

5 The basic structure of the fungi:
The basic structural unit of fungi is either a chain of tubular, filament-like cells, termed a hypha or hyphae (plural) or an independent single cell. The living body of a fungus is called a mycelium which is made up of a branching network of filaments known as hyphae. Fungal cell differentiation is no less complicated than is found in plants or animals, but it is different. Many fungal pathogens of humans and animals change their growth form during the process of tissue invasion. These dimorphic pathogens usually change from a multicellular hyphal form in the natural environment to a budding, single-celled form in tissue

6 In most multicellular fungi the vegetative stage consists of a mass of branching hyphae, termed a mycelium. Each individual hypha has a rigid cell wall They are filamentous, gram positive and bear fruiting bodies called spores. Can exist as single cells or chains of cells.

7 History of taxonomy All organisms were classified to: Plants Animals Fungi were classified with plants: Immobility Cell wall By the Development of the electron microscope in 1995s, Fundamental differences between the bacteria and fungus were discovered: Although in many ways fungi resemble bacteria (neither has chlorophyll), they are unlike bacteria in: Composition of the cell walls. Reproducing through sporulation or spore formation. So it was classified again into 5 Kingdoms: Bacteria. Protista . Animalia Fungi Plant

8 Importance of the fungi:
Fungi are abundant in the human environment, and can found every where. Most of them lead a saprophytic life, living on dead matter (e.g. Mushrooms). Fungal infections are assuming a greater importance, why!! This because of their increasing incidence among: Transplant patients Immunocompromised AIDS In the last 20 years extraordinary changes in fungal infection pattern!! New pathogens have emerged Increasing international travel use wrongly of antimicrobial agents

9 Helpful fungi: In every day life
The common bread-mould is a fungus. Mushrooms (a vegetarian fungal protein) Saccharomyces cerevisiae is used to ferment sugar to produce alcohol We also use fungi to produce flavourings and vitamins. Fungi play an essential role in both the Nitrogen and Carbon cycle by breaking down dead organic material. We get some important drugs from fungi such as the antibiotic (penicillin and cyclosporine).

10 Helpful fungi: In Research:
Scientists use several fungi to investigate basic functions that occur in all cells because they are: Simple Easy to grow Some cancer research is done using fungi

11 Why studying medical mycology is important?
In humans, fungi cause skin infections such as ringworm and athlete's foot. They also cause several deadly diseases which can be hard to treat. Most patients with deadly fungal diseases do not have a fully functional immune system. Leukaemia AIDS Drugs to suppress their immune system because of organ transplantation. 4- Antifungal drugs are often toxic. 5- There is a desperate need for new and better anti-fungal agents.

12 Some basic terms: Fungi (fungus) Hyphae (hypha) = cellular thread Septate = hyphae with cross walls non-septate = hyphae without cross walls Mycelium = complex of hyphae The term mould is generally used to describe a fungus which produces hyphae. The term yeast is generally used to describe a fungus which reproduces by budding.

13 Morphology: Filamentous (mould). Yeast Dimorphic

14 Reproduction 1. Asexual reproduction Budding, fission Asexual spore - mitosis zoospores, sporangiospores. oospores, zygospores, chlamydospores 2. Sexual reproduction sexual spore - meiosis ascospore, basidiospore Some fungi have no sexual reproduction (Imperfect fungi).

15 Yeast Round, oval or elongated unicellular cells. 3-15 µm Few capsulated Reproduction Sexual . Asexual : by budding (blastoconidia or blastospores) May give arise to pseudohyphae Examples of pathogenic yeast: Candida albicans

16 2- Filamentous fungi: Multicellular Form branching filamentous called hyphae Hyphae form mycelium Hyphae may be septate of aseptate Reproduction: Asexual: by Conidia and spore Sexual. Examples of pathogenic moulds Dermatophytes

17 3- Dimorphic fungi: Dimorphism this term is used to describe a fungus which occurs in two different forms (temperature and place), for example, some pathogenic fungi are filamentous in culture and yeast-like in infected tissues. 37°C yeast 20 – 30° C moulds. Examples: Paracoccidioides brasiliensis

18 When fungal infections should be considered?
Prolong fever not responding to antibiotics. Neutropenia Diabetes with ketoacidosis Bone marrow and solid organs transplantation HIV patients Travel or stay in endemic areas.

19 Categories True pathogens – 4 species (dimorphic) – Blastomyces dermatitidis – Coccidioides immitis – Histoplasma capsulatum – Paracoccidioides brasiliensis Opportunistic fungi – Not cause diseases in healthy individuals – Invasive medical procedures – Surgery, implants – Medical therapies • Preexisting condition –inherited defects, AIDS, severe burns, etc •Lifestyle factors –Poor diet, poor hygiene, IV drug abuse

20 Mycoses can be classified according to the site of infection into:
Superficial Subcutaneous Deep (systemic). Other Mycoses

21 General notes: Unlike bacteria colonies, fungal colonies spread rapidly by the hyphae which continue to form more and more new colonies. Rate of growth, color, texture and form of the colony is distinct for each species. Is it useful and harmful, some of them may be harmful or may even be life-threatening to humans (e.g. mycotic meningitis), but never cause wide-spread or endemic disease. Cause complex signs Resistant to antimicrobial agents Found almost everywhere (spores, fungi) Inhalation, trauma, or ingestion

22 Spore formation: Most fungi reproduce by forming spores. When the spores germinate, they send out tube-like projections, called germ tubes, which lead to the formation of branching tube-like structures, called hyphae. . The spores may be produced in many different ways and their size, shape, colour, and manner of production are of value in identifying individual species.

23 The principle types of spore are as follow:
1-Chlamydospore: a rest stage, forms when a cell swells up and develops a thick resistant wall. 2- Arthrospore: a spore forms by septation followed by fragmentation of hyphae. 3- Blastospore: a single vegetative cell of yeast which is produced by budding.

24 4- Conidium: a spore produced externally on a specialized hypae called conidiophore,
the conidium (plural conidia) becomes detached when it mature.

25 5- Sporangiospore: a spore produced within a swollen spherical cell (sporangium) at the end of specialized hyphae called a sporangiophore

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