Detection of cutaneous protothecosis by fluorescence in situ hybridization

Objective: To evaluate the value of fluorescence in situ hybridization (FISH) as a tool for the detection of cutaneous protothecosis. Methods: A mouse model of cutaneous protothecosis was established by subcutaneous injection of Prototheca zopfii. Control mice were injected with Candida albicans, Cryptococcus neoformans or PBS. Skin samples were harvested 7 days after injection and embedded in paraffin for staining and labeling, or put into culture for detection of microorganisms. Skin sections were stained with Periodic acid-Schiff (PAS) and hematoxylineosin (HE). A Prototheca- specific DNA probe was developed and tested on the cultures of Prototheca zopfii, Candida albicans, Cryptococcus neoformans, then used for FISH on skin sections from Prototheca- infected and control mice. Results: All of the 11 mice injected with Prototheca developed cutaneous lesions that were positive for Prototheca upon culturing. The Prototheca FISH probe reacted strongly with cultured Prototheca, but failed to react with cultured Candida albicansor Cryptococcus neoformans. Skin sections from Prototheca- infected mice gave a positive signal with the Prototheca probe, while skin sections from control mice did not. Conclusions: Prototheca in paraffinembedded skin tissue sections can be rapidly and accurately identified by FISH. This new method could be useful in the diagnosis of cutaneous protothecosis in the clinic and in epidemiological studies.