Fungi Flashcards
What are Fungi
*Fungi are non-photosynthetic aerobic eukaryotic organisms that absorb nutrients from their environment
*Could be multicellular, unicellular or dimorphics
*Generation time is in hours
*Mycoses/mycotic infections—infections caused by fungal agents
> 100,000 species of fungi
*500 of these species have been associated with human disease, and no more than 100 are capable of causing infection in otherwise normal individuals
*Others are opportunistic
Characteristics of fungi
- Fungal cells are encased within a rigid cell wall, mostly composed of chitin, mannans, glucans and sometimes cellulose.
*These features contrast with the animals, which have no cell walls, and plants, which have cellulose as the major cell wall component
*So different from the prokayotes (bacteria) - Fungi are heterotrophic
*Lack chlorophyll
*No organic food like plants
*Nutrition by secreting enzymes for external digestion and absorbing the nutrients released from the medium - Fungi are simpler in structure than plants or animals
* There is no division of cells into organs or tissues
* The basic structural unit of fungi is either a chain of tubular, filament-like cells (termed a hypha) or an independent single cell (yeast)
*Sophisticated switch of growth pattern for the dimorphics
*change from a multicellular hyphal form in the natural environment to a budding, single-celled form in tissue
Characteristics
4. Fungi reproduce by means of microscopic propagules called either conidia or spores
*Asexually; spores may be
*large (macroconidia, chlamydospores)
or
*small (microconidia, blastospores, arthroconidia).
*Asexual stage is anamorph
*Sexual reproductive stage is called teleomorph
Characteristics of spores
Spores are:
•Very resistant to heat, cold, acids, bases and other chemicals
•Potent allergens
Classification: Based on Phylogenetics
What are the 3 phyla of fungi that are pathogenic to humans?
*basis of ultrastructural or molecular genetic characteristics
*Kingdom Fungi=> 7 phyla
*Only 3 phyla are pathogenic to humans
*Glomeromycota
*Ascomycota
*Basidiomycota
Glomeromycota
•Formerly Zygomycota
•Usually aseptate with branching hypha (could be pauciseptate)
•The asexual spores, or sporangiospores, are produced inside a closed sac, termed a sporangium, the wall of which ruptures to release them
Sexual reproduction consists of fusion of nuclei from compatible colonies, followed by the formation of a single large zygospore with a thickened wall
•subphylum=>Mucoromycotina
•Order=> Mucorales
•Genus (plural; genera)=> Absidia, Mucor, Rhizomucor, and Rhizopus
•subphylum=> Entomophthoromycotina
•Genera=> Basidiobolus and Conidiobolus
Ascomycota
•Most are septate filamentous
•Asexual reproduction consists of the production of conidia in the conidiogenous cell which is contained in a specialized hyphal structure, termed a conidiophore
•Sexual reproduction results from fusion of nuclei from compatible colonies
•Produces ascospores borne in a saclike structure=> Ascus
Basidiomycota
•Most are septate filamatentous
•Some are yeasts
•Asexual reproduction similar to Ascomycota while others don’t produce at all
•Sexual reproduction is by mating to produce basidiospores on the outside of a generative cell, termed a basidium
• basidiomycetous yeasts with anamorphic stages belonging to the genera Cryptococcus, Malassezia, and Trichosporon
•Filamentous basidiomycetes genus Schizophyllum.
Discuss anamorphic fungi
In the past some anamorphic fungi were termed the Fungi Imperfecti (Deuteromycota) and were divided into several artificial form-classes according to their form of growth and production of asexual reproductive structures
Hyphomycetes
Coelomycetes
Hyphomycetes
•mycelium is septate
•conidia are produced directly on the hyphae or on special hyphal branches called conidiophores
•Genera include: Aspergillus, Cladophialophora, Fusarium, Microsporum, Penicillium, Phialophora, and Trichophyton
Classification Based on ultrastructural cellular form
Yeasts (unicellular)
*Candida spp.
Moulds (multicellular)
*Aspergillus spp.
Dimorphics (both unicellular and multicellular)
*Exist as Yeast or spherules (35-37oC and in tissue) and Moulds (25oC and in the environment)
*Useful for their pathogenicity
*Histoplasma spp.
Classification Based on ultrastructural cellular form
•Yeasts (unicellular)
•Candida spp.
•Moulds (multicellular)
•Aspergillus spp.
•Dimorphics (both unicellular and multicellular)
•Exist as Yeast or spherules (35-37oC and in tissue) and Moulds (25oC and in the environment)
•Useful for their pathogenicity
•Histoplasma spp.
Classification Based on the area of the body affected
*Superficial mycosis e.g Pityriasis versicolor,Tinea Nigra
*Cutaneous mycosis e.g. Tinea Pedis (Athlete’s Foot), Tinea Unguium (Onychomycosis (nail infection)), Tinea Corporis, Tinea Cruris, and Tinea Manus( gives rise to
the annular lesions of ringworm), Tinea Capitis and Tinea Barbae (scalp ringworm)
*Subcutaneous mycosis e.g. SPOROTRICHOSIS, CHROMOBLASTOMYCOSIS
*Systemic/endemic mycosis e.g. COCCIDIOIDOMYCOSIS, HISTOPLASMOSIS, BLASTOMYCOSIS and PARACOCCIDIOIDOMYCOSIS
*Opportunistic mycosis- Usually organisms of low pathogens which produce disease only under conditions of lowered immunity eg. candiasis
Characteristics of Mycotic infections
•Presence of fungi in clinical sample not necessarily confirmation of true infection
•Severity depends mostly on the immunologic status of the host
Most pathogenic fungi:
•Do not produce toxins
•Show physiologic modifications during a parasitic infection
•Are thermotolerant,
•are able to withstand many host defenses
•can resist the effects of the active oxygen radicals (respiratory burst) released during phagocytosis
•Mycotic diseases are generally not communicable from person-to-person
Three main groups of Clinical Syndromes
•Mycotoxicosis
•Hypersensitivity diseases
•Colonisation with eventual disease
Mycotoxicosis
•Secondary to ingestion of fungal toxins
•Most of these are accidental
•Ergot alkaloids of Claviceps purpurea
•tissue inflammation, necrosis and gangrene
•Aflatoxin of Aspergillus flavus
•liver damage and carcinogenesis
