CZAPEK-CASEIN 50-PERCENT GLUCOSE (CZC50G) - A NEW MEDIUM FOR THE IDENTIFICATION OF FOODBORNE CHRYSOSPORIUM SPP

A new medium Czapek Casein 50% Glucose agar (CZC50G) has been develope d, on which the four foodborne Chrysosporium spp., C. xerophilum, C. i nops, C. farinicola and C. fastidium can be distinguished by differenc es in growth rates and colony morphology. Chrysosporium xerophilum and C. inops both produced dense white colonies, but C. xerophilum grew f aster than C. inops, 22 mm in 14 d compared to 9-12 mm in 14 d at 25 d egrees C. Some isolates produced a yellow or red reverse due to the re action of ferric ammonium citrate incorporated in the medium with a fu ngal metabolite. Chrysosporium farinicola and C. fastidium both grew p oorly on this medium and produced sparse colonies: C. farinicola grew faster. Electron micrographs of arthroconidia with a cryo-scanning ele ctron microscope showed thickening of the spore walls in C. inops but not in C. xerophilum. The aleurioconidia of C. farinicola and C. fasti dium were different in shape. The differences in colony morphology and growth rate on CZC50G reflected these differences and demonstrated th at these four species could be distinguished easily on CZC50G.