| BackgroundTrichosporon is a genus of adelomycete，a class of blastomyces，Cryptococcales，Saccharomycetaceae that is common in nature and a member of the normal flora of the mouth,skin, and nails. It causes superficial infections and systematic or disseminated trichosporonosis，It can found mainly in immunocompromised patients or patients with cancer, respiratoryinsufficiency, chronic renal insufficiency, underlying hematologicmalignancies,diabetes,cirrhosis and AIDS. The main predisposing conditions were antibiotic therapy,immunosuppressive therapy, corticoids ,chemotherapy,mechanical ventilation, catheter, urethralcatheterization, transplant, granulocytopenia, surgical procedures and continuous ambulatoryperitoneal dialysis. There is also report that healthy persons are infected with this pathogen tocause systemic infection. Trichosporon asahii is the most common cause of fatal disseminatedtrichosporonosis.Researchs show despite the use of antifungal drugs to treat trichosporonosis, infection isoften persistent. T.asahii of study in pathogenic mechanisms, virulence genes and resistancemechanisms is not clear, and resistance to the vast majority of antifungal drug, which causedisseminated or systemic infection and a high mortality rate once invading the body. Therefore,to explore invasion and infection mechanism of T.asahii is particularly important. Antifungalagents used for patients or in research play major role in the fungal cell membrane, cell wall,nucleic acid ,protein synthesis and mitochondria function. The requirement for a new generationof antifungal agents is growing due to development of resistance in the fungal strains as well asthe undesirable side effects caused by some of the current therapeutics. Clinical application ofsome of the drugs in current is limited due to resistance or toxic side effects, or due to theprohibitively high cost of the treatment. The oxidative stress responses in pathogenic fungi hasbecome an hot area of research. Oxidative stress generated by the host causes morphological andphysiological damage in the fungal cells, for example, ROS damage intracellular proteins, lipids,DNA and result in serious structural destruction. ROS injuries is extremely important to clear thepathogen, and pathogens through the ability of the morphological changes to withstand oxidativedamage may lead to the success of immune escape. Accordingly, the use of ROS and oxidativestress may be an effective way for antifungal. ObjectiveIn this study, we monitored in vitro effects of exposure to hydrogen peroxide, diamideand menadione on growth and development of a clinical isolate and an environmental isolate ofT. asahii, obtained commercially.Methods1 Three different concentrations of oxidants were added to the potato dextrose-agar medium(PDA) which were inoculated with suspension from clinical isolates andenvironmental isolates ,observing strain morphous from the whole when incubated for 5 days.2 Growth of cultures was monitored in yeast extract-peptone-dextrose (YPD) liquidmedium containing increasing concentrations of the three oxidants and incubated with shaking at150 rpm for 72 h. Cell and colony morphologies of these cultures were recorded bylight microscopy after staining with lacto-phenol cotton blue staining.3 Mycelia of the two isolates grown on PDA medium containing the intermediateconcentration of the three oxidants were collected after incubation for 48h and recorded byscanning electron microscopy (SEM) to observe strain morphous.Results1 A concentration-dependent decrease in growth and colony diameter was seen in thepresence of oxidants. The average cell and colony diameter of environmental isolate of T.asahiiwas smaller than that of clinical isolate of T.asahii under the control conditions and it wascomparatively more sensitive to the oxidants.2 Cell morphous observed by light microscopy .In liquid media cultures of both isolatesof T. asahii, exposure to oxidants resulted in concentration-dependent development delays,reduction in the number of hyphae and germ tubes, conversion of wrinkled surface to smoothsurface, spore hypoplasia, and occasionally cytoplasm shrinkage seen in larger spores.3 Cell morphous observed by SEM. The control of clinical isolates of T.asahii showedwrinkled mycelium without any smooth surface, and the average cell diameter was about 2μm.After exposure to one of the oxidants, cell wall damage was seen and surface wrinkles on thehyphaes disappeared. The hyphaes appeared smooth and smaller with some cytoplasmic spillover.The control of environmental isolate of T.asahii showed large chains of spores connected by afilament, with a tomentose surface and some joint spores. The average diameter was about 3μm.Exposure to the oxidants resulted in pitting and atrophy of the cell wall, absence of microvilliand cytoplasmic spillover. The link of spore chains appeared to be fractured. The morphological changes were highest in presence of menadione and least in the presence H2O2at theconcentrations tested.ConclusionsThe higher the oxidant concentration, the fewer the number of two strains, and theconcentration reaches a certain value, the two strains no longer grow. Three oxidants affect thegrowth and development of the clinical isolates and environmental isolates of T.asahii whichspores state conver to mycelium state . The environment isolates of T. asahii have a greatermodification. We suppose that T. asahii hold the antioxidant mechanism, when oxidation effectexceed antioxidant effect, the strains decrease in the number, or no longer grow. |
PDF Full Text Request