Multiple cutaneous infections caused by Prototheca wickerhamii

Prototheca species are a group of organisms ubiquitously existing in nature but have become a pathogenic threat to public health, which has aroused wide attention. Species identification and antifungal susceptibility have essential and valuable meanings to clinical diagnosis and treatment.

A case of an 84-year-old patient who had suffered from multiple cutaneous infections was reported. Tissue samples of the damaged skin were collected from the patient and used for microscopic examination and tissue culture. Staining methods, the VITEK system with YSD card and the molecular identification method based on partial mitochondrion-encoded cytochrome b (cytb) gene amplification and sequencing were used for species identification. Antifungal susceptibility testing was completed by using YeastOne plate.

The patient had type II diabetes mellitus. Round, grape-like, and scattered morula forms were observed under the microscope in bright blue with lactophenol cotton blue staining and in green fluorescence with fungus fluorescence staining. Yeast-like colonies were grown on both the blood plates and the Sabouraud agar. P wichehamii was identified and presented resistance to three echinocandins, fluconazole, and 5-fluorocytosine, while was susceptible to amphotericin B, posaconazole, itraconazole, and voriconazole.

Our result revealed that an old patient with diabetes mellitus might be a dangerous population of cutaneous protothecosis. It also highlighted the contribution to microbial methodology on the diagnosis and treatment of such rare fungus infection.