الفهرس 
Malassezia yeastOnly 14 pages are availabe for public view
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Abstract
Within the last decade, the genus malassezia has received considerable attention from dermatologists and other clinician, this group of yeasts, long known to be the causal agents of PV, is also increasingly being associated with the causation of folliculitis, papillomatosis, and invasive human infection, as well as potential immunogenic triggering of atopic dermatitis (AD), seborrhiec dermatitis (SD), and dandruff. Malassezia species are listed among the new and emerging yeast pathogens.
Gueho et al (1996) recognized seven distinct species within the genus , namely M.furfur, M.pachydermatis, M.globosa, M.obtusa, M.restricta, M.slooffiae and M.sympodialis, furthermore four new species were included in this genus, namely M.dermatis, M.yamatonesis, M.japonica and M.nana.
Pityriasis versicolor (PV) is a common, benign, recurrent cutaneous disease. Its name describes its main characteristics: the onset of maculae and patches of variable color, from white to pink, or brown. The lesions are variably located on the upper trunk, chest, back, and shoulders and can spread to the neck, face, and arms. is usually asymptomatic, although some patients develop moderate or even severe pruritus.
The clinical diagnosis of PV is very easy for an experienced dermatologist in most cases, however it could be confirmed by direct examination with KOH, Wood’s light can also be used to confirm the diagnosis, Skin biopsy is rarely necessary for diagnosing PV. The culture is not necessary for routine diagnosis, but it is indispensable to recognize the species involved in the disease, as well as those present in the normal cutaneous flora.
This work was designed as a case study on 30 patient complaining of PV of various clinical types, All cases had not received topical antifungal treatment for at least two weeks or systemic antifungal for at least one month before the samples were taken.
Clinical assessment was done for every patient. Two samples were obtained from each case, from skin lesion part of scales was used for microscopic examination, using potassium hydroxide (10-20%) and the other part was used for culture of Malassezia species. also from healthy looking skin two cellophane tape were used, one for KOH and the second for culture directly on the plate containing media.
The samples were grown on specific culture media ; Dixon’s medium, with chloramphenicole , cyclohexamide. Isolates were then identified and differentiated by macroscopic, microscopic and physiological characteristics.
Macroscopically; We identified three species of Malaasezia from samples of skin lesion; M.furfur (60%) which appears as creamy, umbonate, smooth, soft colonies ,M.sympodialis (10%) appears as creamy-buff shiny, soft, smooth colonies and M.golobosa (20%) which appears as cream- buff, rough, coarse colonies. The same species, but with different percentage were identified from culture of non-lesional skin, M.furfur (13.3%), M.sympodialis (3.3%) and M.golobosa (3.3%).
Microscopically after Gram’s stain; M.furfur appeared as numerous yeast cells with board base buds (bottle shaped), M.sympodialis appearedas numerous small oval yeast cells with Sympodial condition and M. golobosa appeared as numerous large rounded yeast cells with narrow base buds.
Physiological reactions revealed that:
-The catalase test was positive in all M. isolates that means that M.restricta was not isolated from any of the specimens as it is the only species that give negative reaction with catalase test .
- In Tweens assimilation test, M. furfur assimi¬lated all Tweens, M. sympodialis failed to assimilate Tween 20 , , while no assimilation occurred with M. globosa.
-In Tryptophan test only M. furfur gave a positive reaction, while the other species give negative reaction.
In our study, PV was of highest prevalence in twenty to thirty years old age group, with no difference in development of it among both sexes, the commonest sites were neck, chest, and back.
from our statistically analysed results we found that there was a positive correlation between the isolated species from both PV lesion and healthy looking skin, M.furfur was the predominant in culture from both lesional and non-lesional skin, this indicate that M.furfur is regularly present in its yeast phase in the skin of our healthy population , produces the clinical lesions of PV when developing its mycelial phase.