Growth of Trichosporon asahii in presence of the oxidants, hydrogen peroxide, diamide and menadione

The opportunistic pathogenic fungus, Trichosporon asahii easily causes rare skin and disseminated infections in the skin and internal organs in immunocompromised patients, particularly, those with AIDS or cancer or those who have received organ transplant are also susceptible to T. asahii infection. In this study, we monitored theeffects of three oxidants exposure to hydrogen peroxide, diamide and menadione on growth and development of a clinical isolate and an environmental isolate of T. asahii in vitro, obtained commercially. Growth of cultures was monitored in potato-dextrose agar (PDA) medium or yeast extract-peptone-dextrose (YPD) liquid medium containing increasing concentrations of the above oxidants. Cell and colony morphologies of these cultures were recorded by light microscopy and scanning electron microscopy (SEM), respectively. A concentration-dependent decrease in growth and colony diameter was seen in the presence of with oxidants concentration increase. The three oxidants all had the effect of inhibition and destruction of T. asahii. Under the same concentrations, the killing effect of three oxidants to T. asahii was different; menadione was strongest, followed by diamide and hydrogen peroxide was the weakest (compared with clinical isolate, the environmental isolate was more sensitive to the oxidants. All the three oxidants made the changes to T. asahii’s morphosis and structure, which resulted in its hypoplasia, aplasia and morphological conversion; menadione had stronger damaging effect. The average cell and colony diameter of the environmental isolate was smaller than that of the clinical isolate under the control conditions and it was comparatively more sensitive to the oxidants. In cultures of both isolates, exposure to oxidants resulted in concentration-dependent development delays, reduction in the number hyphae and of germ tubes, conversion of wrinkled surface to smooth surface, spore hypoplasia, and occasionally cytoplasm shrinkage seen in larger spores. Among the three oxidants tested, menadione had a comparatively higher damaging effect.   Key words: Trichosporon asahii, oxidant, morphology.