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01/09/1444 YEASTS OF CLINICAL SIGNIFICANCE By Abdulfatah albakkosh 1 . Candida albicans • Candida albicans is the most prevalent yeast isolate and the causal agent of candidiasis, which is a term for Candida infections. • Candida albicans is a natural component of the flora of the respiratory, gas...

01/09/1444 YEASTS OF CLINICAL SIGNIFICANCE By Abdulfatah albakkosh 1 . Candida albicans • Candida albicans is the most prevalent yeast isolate and the causal agent of candidiasis, which is a term for Candida infections. • Candida albicans is a natural component of the flora of the respiratory, gastrointestinal, and female genital tracts. • The majority of adult infections are endogenous, while newborns receive most of their infections from their mothers (exogenous infections). 1 01/09/1444 Most frequent species Candida albicans Candida glabrata Ecology Commensal yeast from the digestive ,genital and respiratory tract mucosa,represent more than 75% of yeasts isolated in humans Digestive mucosa and urogenital tract Candida parapsilosis Candida tropicalis skin Soil, water,digestive tract, urinary and respiratory tract Candida krusei Food ( Dairy, beer) c. Types of candidiasis 1) Thrush (oral cavity) 2) Vulvovaginitis (vagina) 3) Onychomycosis (nail infections) 4) Paronychomycosis (cuticle infections) d. C. albicans can also cause systemic infections, including meningitis, UTIs, and heart and lung infections. e. Burns, wounds, diabetes, antibiotic medication, pregnancy, leukaemia, and immunological disorders are all common risk factors for Candida infections. 2 01/09/1444 Thrush 3 01/09/1444 Culture characteristics 1) C. albicans grows on most fungal media as well as sheep blood, chocolate, and eosin-methylene blue agars. 2) On cornmeal agar with Tween 80, isolates produce chlamydospores. 4 01/09/1444 3) Biochemical tests a) A positive germ tube can be used as a starting point for identifying C. albicans ; however, not all strains are positive. C. Dubliniensis is also positive and will form chlamydospores. b) Except for C. krusei, • all Candida are urease negative. Not all strains of C. krusei are urease positive. c) Candida spp. are inositol negative. 2. Cryptococcus neoformam • a. Causes cryptococcosis, which can produce a mild to moderate pulmonary infection; however, in the immunocompromised patient, cryptococcosis can lead to systemic infections and meningitis. • Cryptococcosis is also associated with prostate and tissue infections. • b. C. neoformans can be spread through the droppings of bats, pigeons, and other birds, as well as through contaminated vegetables, fruits, and milk. 5 01/09/1444 c. Identifying characteristics for direct specimens 1) Yeast cells appear round and irregular in size when stained with Gram stain. 2) Hematoxylin and eosin stains are used to show capsules in tissue. 3) Direct antigen test for cryptococcal antigen: Performed on CSF and serum specimens d. Culture characteristics 1) Brown to black colonies on bird seed or caffeic acid agars 2) Only forms blastoconidia 6 01/09/1444 3) Biochemical tests a) Positive for urease and phenol oxidase b) Inositol metabolism c) Negative for nitrate reduction 7 01/09/1444 3. Trichosporon a. T. beigelii was the name formerly used for the species in the genus Trichosporon causing most human infections. Several other species are now associated with human infections, including the human hair infection white piedra and rarely the systemic disease referred to as trichosporonosis. b. Trichosporon spp. can be isolated from the soil, animals, and humans. white piedra 8 01/09/1444 c. Culture characteristics 1) Trichosporon spp. form cream-colored, smooth colonies on solid Media in about 1 week. 2) Hyaline hyphae with blastoconidia and arthroconidia are produced. 9 01/09/1444 Microscopic appearance of Trichosporon species on lactophenol cotton blue preparation showing the presence of both blastoconidia and arthroconidia 10 01/09/1444 3) Biochemical tests a) Positive for urease b) Can assimilate some carbohydrates. 4. Rhodotorula a. Rhodotorula spp. are found in moist environments such as on shower curtains and toothbrushes. They have also been isolated from soil and dairy products. Although they have been associated with hospital acquired infections, they are generally considered commensals or contaminants. b. Rhodotorula resemble the Crytpococcus, but they are inositol negative. Some species produce a pink pigment. 11 01/09/1444 Rhodotorula glutinis, SABDX (top). 12