First case of human protothecosis in Canada: laboratory aspects

A case of bursitis due to Prototheca wickerhamii is briefly reported. In histological sections the organism stained well with fungal stains, grey with silver methanamine and red with periodic acid Schiff reagent. This unicellular achlorophyllous alga was studied on common laboratory media. The characterization of the Prototheca sp. depends largely on wet mount microscopic examination from broth or agar cultures which ensures the observation of endosporulation and a consistent absence of budding. Otherwise the growth rate and the pasty white colonies may lead to an erroneous identification, most likely as a Cryptococcus sp. P. wickerhamii lends itself very well to standard physiological tests used for the identification of yeasts. The strain was found insensitive to 5-fluorocytosine. The MIC of amphotericin B was 0.15 microgram/ml.