University:
American Career College
Course:
MA700 | Clinical Procedures and Pharmacology
Academic year:

2021
Views:

176

Pages:

51
Author:

VNever

1 The Fungi represent one of the five kingdoms of organisms classified, according to Whittaker (1969). Monera: prokaryote, bacteria Protista: eukaryote, protozoa Plantae: eukaryote, trees Animalia: eukaryote, animals and human Fungi: eukaryote, mushrooms, yeasts, molds Whittaker 1969 • The actinomycetes, which are true bacteria, have traditionally been studied by medical mycologists because, like fungi, they have mycelial forms and cause similar diseases. • The earliest known record of a mycotic infection is that in the Atharva Veda in India (about 2000-1000 BC), of mycetoma of the foot. Common terms Fungus (fungi) Mushroom Mycology Medical Mycology Mycosis (pl. Mycoses)=Fungal infection(s) Opportunistic vs. true pathogens  Opportunistic fungi: fungi that are normally commensal or do not harm human but can cause disease when the host’s resistance is low.  True fungal pathogens: fungi that cause disease in human, regardless of its immune system status. What are fungi? Non-motile eukaryotic organisms, with real nucleolus and cell wall, without chlorophyll (heterotroph) Reproduce by structures named conidia/spore Ergosterol is the specific sterol of fungi in their cell membrane. human: cholesterol, plants: phytosterol Two distinct morphological forms: yeast, mold Dimorphic fungi: Those that can exist in the form of both mold and yeast.  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. Nutrition • 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. • Fungi are heterotrophic. This means that they are lacking in chlorophyll and cannot make their organic food, as plants can, through photosynthesis Morphology Yeast • Single cell • Round, oval • Reproduction using budding or binary fission • Some could produce pseudohyphae Morphology Mold/mould Filamentous form Hyphae (filaments) Mycelium: branched hyphae Apical growth Septate/non-septate (aseptate) Hyaline/pigmented Morphology Colony: A colony is defined as a visible mass of fungi all originating from a single mother cell.  Yeast colonies typically have a smooth (glabrous) texture. The colonies of Candida species are generally creamy white.  The texture and color of mold colonies can vary from species to species. Reproduction Fungi reproduce by means of microscopic propagules called either conidia or spores. Many fungi produce conidia that result from an asexual process. Asexual conidia are generally short-lived propagules that are produced in enormous numbers to ensure dispersion to new habitats. Reproduction Many fungi are also capable of sexual reproduction. Sexual reproduction: plasmogamy >> karyogamy >> meiosis The sexual stage of a fungus is known as the teleomorph, and the asexual stage is the anamorph. Reproduction Fungi are classified based on their sexual reproduction. oZygomycota: produce zygospore oAscomycota: produce ascospore oBasidiomycota: produce basidiospore oDeuteromycota (imperfect fungi): no known sexual spore Sporangiospore • Asexual spore • Produced by Zygomycota e.g. Rhizopus species, Mucor species Arthroconidia • A type of fungal spore typically produced by segmentation of pre-existing fungal hyphae Chlamydoconidia/chlamidospore • Thick-walled large resting spore • Might be terminal, intercalary, or sessile • Important for identification of Candida albicans from non-albicans species Microconidia and macroconidia • Some fungi produce macro and microconidia, which are conidia of two different sizes produced by one fungus in the same manner. • Macro- and micro- refer to large and small conidia, respectively. Germ tube Germ tubes represent the initiation of hyphal growth and arise directly from the yeast cell or conidia. They have parallel walls and at their point of origin; they are not constricted  Mycetismus: Poisoning by toxic mushrooms.  Mycotoxicosis: consequences of consumption of cereals etc. that are previously contaminated by toxigenic saprohpytes.  Aspergillus flavus: aflatoxins  Fusarium : fumonisin  Fungal infections:  Allergy and asthma Superficial and cutaneous fungal infections • Tinea versicolor • Otomycosis • Keratomycosis • Tinea nigra • Piedra • Dermatophytosis • Erythrasma Subcutaneous and systemic fungal infections • Sporothricosis • Candidiasis • Mycetoma • Aspergillosis • Chromoblastomycosis • Cryptococcosis • Entomophthoromycosis • Mucormycosis • Lobomycosis • Saprobe: An organism that uses dead organic matter as a source of food. • Although in normal conditions, they are not able to cause infection, however, they could cause a set of life-threatening infections among immunocompromised patients. • They are common contaminants in laboratory. Classification of saprophytic molds • Septum: septate or aseptate • Color: hyaline or pigmented (colored/dematiaceous) Aspergillus species • Aspergillus species are ubiquitous saprophytes. • There are more than 200 Aspergillus species, with more than 30 known to be human pathogens. • The fungus is also commercially important. A. niger is the source of enzymes such as amylases, lipases, and proteases and is used to produce the majority of the world’s citric acid. Aspergillus species • Significant species • A. fumigatus, A. flavus, A. terreus, A. nidulans, A. niger, A. clavatus, and A. versicolor • Microscopic appearance: • Hyaline • Septate • Conidiophore > vesicle > phialide > conidia Aspergillus niger Aspergillus flavus Penicillium species • They could cause some infections in human. • Common contaminants of apples juice by patulin. • The source of some antibiotics such as penicillin and griseofulvin. • Microscopic appearance: • Hyaline • Septate • Conidiophore > metula > phialide > conidia Penicillium species Fusarium species • Some of them can cause lethal human infections. • Contaminants of food and feedstuff like maze by fumonisin. • Microscopic appearance: • Hyaline • Septate • Two different types of conidia: • Macroconidia: fusiform (diagnostic) • Micoconidia Fusarium species Scopolariopsis species • The cause of human keratomycosis and onychomycosis. • Microscopic appearance: • Hyaline • Septate • Conidiophore > annelide > lemon-shaped conidia Scopolariopsis species Scopolariopsis species Rhizopus species • The most common causes of mucormycosis. • Microscopic appearance: • Hyaline • Aseptate • Sporangiophore > sporangium > sporangiospores • Rhizoid Rhizopus species Mucor species • Common causes of mucormycosis. • Microscopic appearance: • Hyaline • Aseptate • Sporangiophore > sporangium > sporangiospores • Rhizoid is absent. Mucor species Alternaria species • Common contaminants in laboratory • Less common human pathogens • Microscopic appearance: • Pigmented (colored/brown) • Septate • Chains of conidia which have both transverse and longitudinal septations Alternaria species Cladosporium species • Common contaminants in laboratory • Less common human pathogens • Microscopic appearance: • Pigmented (colored/brown) • Septate • Conidia in general are elliptical to cylindrical in shape, pale to dark brown in color. They occur in branching chains that readily disarticulate. Cladosporium species Geotrichum species • A common saprophyte and part of normal human flora. • Could cause some mucosal infections mimicking candidiasis in appearance. • A known producer of arthroconidia Rhodotorula species • Laboratory contaminants. • Uncommon human pathogens. • Some species have diagnostic colony color.