Czapek casein 50% glucose (CZC50G): a new medium for the identification of foodborne Chrysosporium spp.

A new medium Czapek Casein 50% Glucose agar (CZC50G) has been developed, on which the four foodborne Chrysosporium spp., C. xerophilum, C. inops, C. farinicola and C. fastidium can be distinguished by differences in growth rates and colony morphology. Chrysosporium xerophilum and C. inops both produced dense white colonies, but C. xerophilum grew faster than C. inops, 22 mm in 14 d compared to 9-12 mm in 14 d at 25 degrees C. Some isolates produced a yellow or red reverse due to the reaction of ferric ammonium citrate incorporated in the medium with a fungal metabolite. Chrysosporium farinicola and C. fastidium both grew poorly on this medium and produced sparse colonies: C. farinicola grew faster. Electron micrographs of arthroconidia with a cryo-scanning electron microscope showed thickening of the spore walls in C. inops but not in C. xerophilum. The aleurioconidia of C. farinicola and C. fastidium were different in shape. The differences in colony morphology and growth rate on CZC50G reflected these differences and demonstrated that these four species could be distinguished easily on CZC50G.