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Clinical Microbiology made easy 2

PART 2. FUNGI.CHAPTER 20. THE FUNGI.As "budding" doctors in the modern world of AIDS, organ transplantation, and modern chemotherapy, you.will treat an unprecedented number of immunocompromised patients. With their lowered cell-mediated immunity, there is a dramatic increase in the incidence of.virtually every fungal infection! You will commonly see.fungi that used to be exceedingly rareFungi are eucaryotic cells, which lack chlorophyll, so.they cannot generate energy through photosynthesisThey do require an aerobic environment. After discussing the following crucial terms, we will discuss the.categories of fungi pathogenic to humansYeast: Unicellular growth form of fungi. These.cells can appear spherical to ellipsoidal. Yeast reproduce by budding. When buds do not separate, they can.form long chains of yeast cells, which are called.pseudohyphae. Yeast reproduce at a slower rate than.bacteriaHyphae: Threadlike, branching, cylindrical, tubules.composed of fungal cells attached end to end. These.grow by extending in length from the tips of the tubulesMolds (also called Mycelia): Multicellular colonies.composed of clumps of intertwined branching hyphaeMolds grow by longitudinal extension and produce.sporesSpores: The reproducing bodies of molds. Spores are.rarely seen in skin scrapingsDimorphic fungi: Fungi that can grow as either a.yeast or mold, depending on environmental conditions.and temperature (usually growing as a yeast at body.temperatures)Saprophytes: Fungi that live in and utilize organic.matter (soil, rotten vegetation) as an energy source.Cell wall: Surrounding the cell membrane is the cell.wall, composed mostly of carbohydrate with some protein. Fungal cell walls are potent antigens to the human.immune systemCapsule: This is a polysaccharide coating that surrounds the cell wall. This antiphagocytic virulence factor is employed by Cryptococcus neoformans. The.capsule can be visualized with the India ink stainFig. 20-1. It is helpful to organize the human fungal.diseases by the depth of the skin that they infect.SUPERFICIAL FUNGAL INFECTIONSPityriasis versicolor and tinea nigra are extremely superficial fungus infections, whose primary manifestation is pigment change of the skinNeither of these cause symptoms and will only come.to your attention because skin pigment change is.noted!!! Both are named for their respective skin.manifestations:.Pityriasis versicolor ( multicolored).Tinea nigra (black colored)1) Pityriasis versicolor (also called tinea versicolor) is a chronic superficial fungal infection which.leads to hypopigmented or hyperpigmented patches.on the skin. With sunlight exposure the skin around the.patches will tan, but the patches will remain white. This.infection is caused by Malassezia furfur2) Tinea nigra is a superficial fungal infection that.causes dark brown to black painless patches on the soles.of the hands and feet. This infection is caused by Ex-FUNGAL MORPHOLOGYCertain morphologic characteristics serve as virulence factors as well as targets for antifungal antibioticsCell membrane: The bilayered cell membrane is the.innermost layer around the fungal cytoplasm. It contains sterols (sterols are also found in the cell membranes of humans as well as the bacteria Mycoplasma)Ergosterol is the essential sterol in fungi, while cholesterol is the essential sterol in humans. The antibiotics amphotericin B and nystatin bind to ergosterol.and punch holes in the fungal cell membrane, while ketoconazole inhibits ergosterol synthesis.ophiala werneckii.Diagnosis of both infections is based on microscopic.examination of skin scrapings, mixed on a slide with.potassium hydroxide (KOH). This will reveal hyphae.and spherical yeast, as the KOH digests nonfungal.debris. Malassezia can look like spaghetti (hyphae) with.meatballs (spherical yeast)Treatment of both consists of spreading dandruff.shampoo containing selenium sulfide over the skinThis is an inexpensive and e