Morphology of Penicillium marneffei under oxidative stress in vitro

Penicillium marneffei is an intracellular pathogen; the mechanism allowing it to survive under oxidative stress remains unclear. For a better understanding of the response of P. marneffei to oxidative stress, the change in ultrastructure of this fungus before and after treatment with hydrogen peroxide was examined. A bamboo rat isolate and human isolate of P. marneffei were cultured on PDA at 25 °C and on BHI agar at 37 °C for 7 days respectively, with and without hydrogen peroxide; the morphology of strains was examined by optical microscopy and transmission electron microscopy. While comparing the human isolate with the bamboo rat isolate cultured without hydrogen peroxide, it showed no significant difference in ultrastructure. Microbodies were seen under transmission electron microscope in the yeast form, but could not be seen in mould form. After the strains were cultured with hydrogen peroxide, the mould form produced more rose red pigment; organelles of the fungal cells had been involved at different levels. Furthermore, the mould form of the human isolate with decreased conidia production and the yeast form with apoptosis could be observed. These results indicated that different strains of P. marneffei may have different levels of power to survive under oxidative stress.