Mycology Classification & General Properties of Fungi Lec. 2 PDF

Mycology Classification & General Properties of Fungi Lec. 2 Systematic Classification REPRODUCTIVE STRUCTURES ASEXUAL & SEXUAL SPORES REPRODUCTION Most fungi reproduce Asexually and Sexually by spores  ASEXUAL reproduction is most common method & produces genetically identical organisms Fungi re...

Mycology Classification & General Properties of Fungi Lec. 2 Systematic Classification REPRODUCTIVE STRUCTURES ASEXUAL & SEXUAL SPORES REPRODUCTION Most fungi reproduce Asexually and Sexually by spores  ASEXUAL reproduction is most common method & produces genetically identical organisms Fungi reproduce SEXUALLY when conditions are poor & nutrients are scarce Sexual spores are rarely agents of human disease. asexual spores that are generally responsible for initiating human infection. Fungal Reproduction Sporulation (process of making spores) is the principal means by which fungi reproduce and spread through the environment. Fungal spores are metabolically dormant, protected cells. They can be borne by air or water to new sites, where they germinate and establish colonies. Perfect fungi: Fungi that are capable of sexual reproduction (meiotic reproduction), which is the teleomorph state. Example: Candida sorbosa. Imperfect fungi: Fungi that lack sexual reproduction, they are represented only by an anamorph state (mitotic reproduction). Example: Aspergillus spp. HYPHAL GROWTH FROM SPORE Germinating spore mycelium Mycelia have a huge surface area  More surface area aids digestion & absorption of food  Vegetative Structures REPRODUCE BY SPORES  Spores may be Formed:  Directly on hyphae  Inside sporangia  On Fruiting bodies Penicillium hyphae Amanita fruiting body Pilobolus sporangia SEXUAL REPRODUCTION  Sexual spores are formed from the fusion of nuclei from two opposite mating strains of the same species.  Haploid 1n hyphae from 2 mating types (+ and -) FUSE (Fertilization)  Forms a hyphae with 2 nuclei that becomes a ZYGOTE (meiotic in origin)  The zygote divides to make a SPORE  Structures that contain sexual spores in fungi are called fruiting bodies + SPORE FORMS Systematic classification Based on sexual spore formation: 5 classes 1. Zygomycetes 2. 3. 4. 5. Perfect fungi Ascomycetes reproduce sexually Basidiomycetes Chytridiomycetes/oomycetes Deuteromycetes (imperfect fungi) Sexual spores Zygospores: Zygote fungi or Bread mold Fungi forming zygospores are called zygomycetes. Zygospores Ascospores: Sac fungi Fungi forming ascospores are called ascomycetes. Ascospore is found in a sac-like structure called an ascus (plural asci). several asci are usually contained in a single large fruiting body. Ascospores inside an ascus Sexual spores Basidiospores: Club fungi Basidiospores are carried on basidium. Fungi forming basidiospores are called basidiomycetes. Mushroom is a common fungal fruiting body that produces basidiospores. Spores formed at the tip of a club like structure called a basiduim (plural, basidia). Basidiospores Oospores: characterized by the production of large flagellated sexual oospores produced by certain aquatic fungi. Fungi forming Oospores are called Oomycetes or Chytridiomycetes Chytrids Deuteromycetes are fungi whose sexual spores are unknown. But, they produce asexual spores. Most fungi causing human infections belong to this group. Asexual reproduction Molds may form either sexual or asexual spores Asexual spores, which are most commonly used in identification, are formed by the aerial mycelium of a single organism by mitosis and cell division THREE TYPES OF ASEXUAL REPRODUCTION  Fragmentation – part of the mycelium becomes separated & begins a life of its own  Budding – a small cell forms & gets pinched off as it grows to full size  Used by yeasts  Asexual spores – production of spores by a single mycelium BUDDING 2 0 Asexual spores Conidia: Asexual reproductive structures are produced either from the transformation of a vegetative yeast or a hyphal cell. Asexual spores ▪ Blastospores consist of a bud coming off the parental cell Blastospores: Produced by budding of the yeast cells. Asexual spores ▪ Conidiospores are produced in a chain at the end of a conidiophore. ▪ Unicellular conidiospores are called microconidia ▪ Multicell conidiospores are called macroconidia Macroconidia Microconidia Arthrospores ▪ Arthrospores are formed by the fragmentation of septate hyphae Asexual spores ▪ Chlamydospores are thick walled spores formed within a hyphae Asexual spores ▪ Sporangiospores are formed within a sac (sporangium) at the end of an aerial hyphae called a sporangiophore Fungi reproduction Life cycle of fungi HUMAN-FUNGUS INTERACTIONS Beneficial Effects of Fungi – Decomposition - nutrient and carbon recycling. – Biosynthetic factories. Can be used to produce drugs, antibiotics, alcohol, acids, food (e.g., fermented products, mushrooms). – Model organisms for biochemical and genetic studies. Harmful Effects of Fungi – Destroy any manufactured material except plastics. – Contamination of food – Animal and human diseases, including allergies. – Toxins produced by poisonous mushrooms and within food (e.g., grain, cheese, etc.) -Plant diseases Fungi as Parasites & Pathogens Clinical Manifestations of Fungal Disease Fungal diseases are grouped in three categories of clinical manifestation Fungal infections Most common mycoses Caused by the presence in the body of either true pathogens or opportunists Toxicoses Acquired through ingestion Occurs when poisonous mushrooms are eaten Allergies Most often result from the inhalation of fungal spores Medical Mycology Mycoses are among the most difficult human diseases to diagnose and treat Signs of mycoses are often missed or misinterpreted Fungi are often resistant to antifungal agents Human mycoses are caused by true fungal pathogens and opportunistic pathogens True or primary fungal pathogen can invade and grow in a healthy, non compromised host. opportunists” cause disease almost exclusively in immune compromised hosts Categories of Fungal Agents Only four fungi are usually considered true pathogens 1 Have the ability to actively attack and invade tissues 2 Exhibit dimorphism (Based on differences in temperature) Thermal dimorphism – grow as molds at 30°C and as yeasts at 37°C Yeast forms are invasive 3 production of enzymes and proteins 4 Endemic to certain regions Antifungal Therapies Mycoses are among the most difficult diseases to heal The injury caused by fungal infections seems to be due primarily to the inflammatory immune responses that are stimulated by the prolonged presence of the fungus. Fungi can often resist the oxidative damage of T cells during cell-mediated immune responses As eukaryotes, fungi are similar to human cells and antifungal drugs can harm human tissues Fungi have ergosterol in their membranes rather than cholesterol and it is often a target for antifungal treatment Side effects can still result, especially with long-term use Antifungal Therapies Amphoterecin B is the ‘‘gold standard” of antifungal agents but also the most toxic Other antifungal agents include various azole drugs, fluorocytosine, and griseofulvin Topical Anitfungals – imidazoles Control of Mycotic Infections Immunization is not usually effective In some cases surgical removal of damaged tissues Prevention limited to masks and protective clothing to reduce contact with spores