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Prototheca spp. are mastitis-causing pathogens that are classified as colorless algae. Prototheca spp. will appear on blood agar as creamy-white or grayish-white pasty colonies after 24 to 36 hours of incubation. Colonies could be confused with coagulase-negative staphylococci or yeast but can be differentiated when Gram staining because Prototheca spp. will exhibit spherical or oval sporangia with or without endospores.
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Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
April 5, 2016