Medical Mycology: BCDT 1031 Module 4

• Module 4 of BCDT 1031 covers Medical Mycology.

Presentation Outline

• Topics include general properties of fungi, morphology, medically important fungi classification, fungal reproduction and metabolism, and pathogenesis of fungal diseases.

Learning Objectives

• Students will be able to define fungi
• Students will also be able to list the different characteristics of fungi, explain their morphology, describe their classification, and discuss their reproduction, metabolism, and pathogenesis of fungal diseases.

Introduction to Medical Mycology

• Mycology is the study of fungi, including yeasts and molds.
• This encompasses genetic properties, biochemical properties, taxonomy, and uses in relation to humans.
• Medical Mycology studies fungi that infect humans.
• Fungal infections can be superficial, cutaneous, subcutaneous, deep mycoses, primary mycoses, and opportunistic mycoses

General Characteristics of Fungi

• Fungi are eukaryotic organisms.
• They possess a rigid cell wall containing mannan, glucan, and chitin.
• Chitin and glucan provide rigidity to the cell wall.
• Mannan is linked to surface proteins.
• Ergosterol is the major membrane sterol in fungi.
• Fungi are non-photosynthetic and lack chlorophyll.

Characteristics of Fungi

• Fungi are heterotrophs, requiring organic substrates as a carbon source.
• Some are saprophytic decomposers, others are symbionts in mutualistic relationships, and some are parasites.
• Fungi reproduce asexually, sexually, or both.
• They can be unicellular or multicellular.
• The natural habitat for fungi is the environment and are omnipresent.
• Most fungi are obligate aerobes, while some are facultative anaerobes.
• They grow best at an acidic pH of below 5.
• Fungi can be macroscopic, microscopic, and dimorphic.
• Fungi differ from bacteria since they are eukaryotic and bacteria are prokaryotic.
• Fungi contain a nucleus while bacteria do not.
• Fungi contain mitochondria and endoplasmic reticulum, unlike bacteria.
• Sterols are present in fungi while cholesterol is within bacteria.
• Chitin can only be found in fungi vs peptidoglycan in bacteria.
• Spores are used for reproduction within fungi and survival in bacteria.
• Replication is binary fission or budding in fungi, and binary fission in bacteria.
• Ribosomes are 80S in fungi and 70S in bacteria.
• All fungi are gram-positive.

Morphology of Fungi

• Fungi are generally larger than bacteria, with individual cell sizes ranging from 1 to 30 µm in diameter.
• Yeast is a monomorphic single-celled fungi
• The shape is round to oval and is usually large, at 5 to 8 µm in diameter.
• Yeast reproduce asexually through fission formation and blastoconidia formation (budding).
• Colonies are often characterized by a smooth surface and mucoid texture.
• Yeasts rarely form pseudohyphae and all are gram-positive.
• Molds are multicellular, filamentous fungi.
• Thallus is the body of the mold, which is made of hyphae.
• Hyphae are cylindrical, tube-like structures and are the basic microscopic unit of molds.
• Hyphae give the macroscopic mold colony its fluffy appearance.
• Mycelium is the intertwined mass of filamentous hyphae in molds.
• Fungal hyphae can be septated or aseptated.
• Septated hyphae have cross-walls with spores that allow cytoplasm migration.
• Aseptate hyphae (non-septate or coenocytic) lack physical boundaries to distinguish individual cells.
• Arial hyphae are fungal filaments that protrude above the surface, producing asexual spores.
• Vegetative hyphae absorb nutrients, exchange water, grow in or on a substrate.
• Vegetative hyphae actively grow and form the main body of the colony.
• Some fungi are dimorphic where they exist as yeast or mold.
• Dimorphism is often regulated by temperature where they can form hyphae at ambient temperature and yeast at body temperature.
• At 37°C, yeast forms in vivo.
• At 25°C mold forms.
• Fungi have complex reproductive strategies with a primary reproductive mode being spores.
• Spores are used for multiplication, survival, genetic variation, and dissemination of fungi.
• Spores are compact, lightweight, and a known cause of allergic diseases.

Fungal Spores

• Fungal spores can be sexual or asexual.
• Asexual spores include sporangiospores and conidiospores.
• Asexual reproduction is called anamorph.
• Anamorph involves mitosis and is often used as the basis of taxonomy in mitospores.
• Medically important fungi produce two types of asexual spores, sporangiospores, and conidia.
• Sporangiospores form by successive cleavages within a sac-like head called a sporangium.
• The sporangium is attached to a stalk called the sporangiophore.
• Sporangiospores are initially enclosed but are released when the sporangium ruptures.
• Conidia are free spores not enclosed by a spore-bearing sac.
• Conidia are the most common asexual spores and come in different forms.
• An arthrospore is a rectangular spore formed when a septated hypha fragments.
• Arthrospores appear square, rectangular, or barrel-shaped with thick-walled cells when mature.
• Chlamydospores are spherical conidia formed by the thickening of a hyphae cell.
• Chlamydospores are released when the surrounding hypha fractures and serve as a survival or resting cell.
• A blastospore is a spore produced by budding from a parent cell, eventually becoming yeast or another conidium.
• Blastospores are also called buds.
• A phialospore is a conidium budded from the mouth of a vase-shaped spore-bearing cell called a phialide or sterigma.
• A porospore is a conidium that grows out through small pores in the spore-bearing cell and is often composed of several cells.
• Microconidia are small and single celled.
• Macroconidia are large, single or many celled.
• Sexual spores involve the fusion of hyphae from two individuals with the process named telemorphs.
• They are produced by the perfect fungi, in meiosis, and involves plasmogamy and karyogamy.
• During sexual reproduction, each parent hyphae has haploid nuclei.
• The fusion of hyphae is called plasmogamy, during which a union of two nuclei-karyogamy
• The offspring possesses slight variations in form and advantageous to the adaptation and evolution of their species.
• Basidiospores are spores formed at the tip of a club-like structure called a basidium (basidia plural) and are formed under the mushroom with gills covered in basidium.
• Ascospores are found in a sac-like structure called an ascus (asci plural).
• Asci are usually contained in a single large fruiting body.
• Zygospores are not associated with well-developed fruiting bodies.
• They are encased in a thick, darkly pigmented wall, which is resistant to extremes in temperature and desiccation.
• Oospores are not associated with well-developed fruiting bodies.
• Oospores are typically large flagellated spores found in aquatic fungi.

Taxonomy

• Fungi are eukaryotes, like animals, which creates therapeutic dilemmas in antimycotic therapy.
• Medically important fungi are classified into phyla based on spore types, hyphae morphology, mode of reproduction, and sexual cycles.
• Mycota, myxomycota, and eumycota are all classification of Kingdom fungi.
• Chytridiomycota, zygomycota, glomeromycota, ascomycota, and basidiomycota are all types of eumycota.
• Phylogenic relationship is based on molecular data and DNA sequence comparison.
• 18S rRNA is widely used as fungal phylogenetic markers for classification.

Fungi Phyla

• Simplest and most primitive fungi
• Appeared during the late pre-Cambrian period more than 500 million years ago
• Mostly aquatic and unicellular with aseptate, coenocytic hyphae.
• Asexual zoospores with single flagella.
• Sexual reproduction is rare but gametes are flagellated isogametes
• Examples including Allomyces and Synchytrium.
• Zygomycota contain aseptate coenocytic hyphae with asexual reproduction using non motile spores produced inside the sporangium.
• They lack flagellated cells and reproduction occurs from -zygospoe formation.
• Examples including Rhizopus, Mucor, and Rhizomucor.
• Mucormycetes can have sexual spores of Zygospores-unenclosed, or asexual spores of Mostly sporangiospores, some conidia.
• Hyphae in Mucormycetes are usually non-septate with free-living saprobes.
• Mostly animal parasites that can be Rhizopus, a black bread mold; Mucor; Lichtheimia and Rhizomucor.
• Order mucorales are rhizopus, mucor, lichthemia, and rhizomucor.
• It results in opportunistic infection in patients with diabetes, leukemia, severe burns, or malnutrition, or rhinocerebral infections.
• Order entomophthorales are basidiobolus, and conidiobolus: Entomophthoromycosis: subcutaneous and gastrointestinal infections

Glomeromycota

• It includes Arbuscular mycorrhizal fungi in symbiotic association with roots of higher plants or bryophytes.
• They have Coenocytic hyphae, are sister group to the Dikarya (Basidiomycota and Ascomycota- Chytridiomycota, zygomycota, Glomeromycota, Ascomycota, and Basidomycota.
• Asexual reproduction occurs by blastospores and Sexual reproduction is absent.
• Examples include Geosiphon pyriformis.
• Basidiomycota is an advances fungus better known as club fungi that forms basidiospores that are formed on club shaped structure called basidium
• Produce Septate well developed mycelium with dolipore septum that produce asexual conidia or sexual basidiospores when formed on basidia
• Includes Agaricus, and Puccinia
• Basidiomycetes reproduce Sexually by means of basidiospores, they lack Incompeltetly septate hyphae, and are plant parasites.
• Examples includes Cryptococcus and Trichosporon, reslting in Cryptococcosis and numerous mycoses.
• Ascomycota are Sac fungi that produce sexual ascospores inside a sac like structure called ascus.
• Reproduction occurs when sexual ascospores undergo cellular division: Apothecium shapes are like cups.
• Has Hyphae with porous septa where ascocarps or fruiting bodies maybe be in Apothecium forming Peziza and Perithecium forming Xylaria.
• Includes Pneumocystidomycetes, has saccharomyces, and eurotiomycetes
• There are 4 classes, with many more than 50% of all name fungal species- with produce sexual and asexual spores by conidiophores
• Peumocystidomycete creates pneumpcystis pneumonia whtile Saccharomycete is commonly found in canidita. .
• Eurotiamycetes contains the dermatophytes and other dimorphs to contain the anamorph genera aspergillus and penicillium
• Sordariomycetesa contains the filamentous ascomycetes and telemorphs that results in telemorphs and is sometimes dematiaceous
• Deutromycota better known as fungi iimperfecte, lack a know reproductive cycle.

Metabolism

• Organisms require energy, carbon, and other nutrients that is transformed by chemical reactions.
• Organism convert nutrient elements or extract chemical energy that help to sustain its structure.
• Autotoph is organism that takes CO2 to form. carbon while heterotroph form organic carbon
• Chemohetetroophs are protozoa, fungi, mamals, and bateria with chemos and fungus
• Includes fungal nutrition to that result symbiotic, Parastic saprophytic
• Saprophytes includes free living organisms with a host , lichens, and mycorhizza
• Pathologies occur in the area after a growth in the body surface.
• The Path has little to no mechanisms in the the body when an fungi is present.

Pathogenesis

• Some fungi are opportunistic and produce disease when the body defense is low.
• Factors include the ability to grow at 37, capsule (cryptococcus), secondary metabloites
• Contributing factors Diabeties, HIV infections, Cancers, and Chemotherapy to causes increase mpoiture

Fungal Diseases Overview

• Caused from a spore in the air that is a Sick building in a high moisture environment.
• May result from toxin from a fungi poisining the mushroom in a aflatoxin infection.
• Super infections can occur: Subcataneous, and Primary infection