Mycology Flashcards
Fungi
Fungi are non-photosynthetic aerobic eukaryotic organisms that absorb nutrients from their environment
•Singular-Fungus!!
•They are definitely not plants
•Could be multicellular, unicellular or dimorphics
•Generation time is in hours
•Mycology –study of fungi
•Mycoses/mycotic infections—infections caused by fungal agents
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Mycology
Study of fungi
Mycology & mycosis
Study of fungi
Infections caused by fungal agents
Characteristics of fungi
They are enclosed in a rigid cell wall made up of chitin
They are heterotrophic
They are simpler in structure than plants and animals
They reproduce by means of microscopic propagules called spores or conidia
This can be asexual ( anamorphic) : large- macroconidia, chlamydoconidia
Small- microconidia, blastospores, antheoconidia or sexual (teleomorphic)
Classes of fungi
Based on Phylogenetics
•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
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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
Classification based on ultra structural cellular structure
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.
Fungi based on area of the body affected
Superficial mycosis
•Cutaneous mycosis
•Subcutaneous mycosis
•Systemic mycosis
•Opportunistic mycosis- Usually organisms of low pathogens which produce disease only under conditions of lowered immunity
Characteristics of mycotoxins 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
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
Hypersensitivity reactions
Hypersensitivity Diseases
•Usually as a result of fungal spores in the air
•In fact one of the indices for air pollution is to measure the fungal spore count
•Trigger off asthmatic attacks, rhinitis, pneumonitis and alveolitis
Quality specimen for mycotic lab investigations
Collection of adequate clinical specimens for investigation
•Good storage
Quality info needed for mycotic lab investigation
Signs and symptoms
•Underlying illness
•recent travel
•previous residence abroad
•the patient’s occupation etc.
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Approaches of mycotic diagnosis
•the microscopic detection of the etiologic agent in clinical material
•its isolation and identification in culture
•the detection of either a serologic response to the pathogen or some marker of its presence, such as a fungal cell constituent or metabolic product
Keratinised dermatologic specimens, sputum and other lower respiratory tract specimens, and minced tissue samples can be examined after treatment with
10–20% Potassium hydroxide (KOH)
Wet preparation
without stain or
•With stain => lactophenol cotton blue, methylene blue (reagents) with low power light microscope
•With stain => calcofluor white (chemical brightener) stains fungal cell wall with fluorescent microscope
India ink (negative staining)- reveals encapsulated Cryptococcus neoformans cells in CSF
•Gram stain
•Giemsa stain and Wright’s stain can be used to detect Histoplasma capsulatum in bone marrow preparations or blood smears
•Papanicolaou stain
Drawbacks of direct microscopy
Quality of the specimen
•Age of the specimen
•the extent of the disease process
•the nature of the tissue being examined
•experience of the microscopist
Histopathologic examination
It depends on abundance and level of distinctiveness of its appearance
Stains for histopathologic examination
Hematoxylin and eosin
•Methenamine-silver (Grocott or Gomori)
•Periodic acid-Schiff (PAS)
Drawback of histopathologic examination
seldom permits the precise fungal genus involved
to be identified
Culture media
Sabouraud’s dextrose agar,
•Potato dextrose agar,
•Potato flakes
•Brain heart infusion specially for fastdious Histoplasma capsulatum
•Additives such as chloramphenicol , gentamicin and cycloheximide to suppress bacteria
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