Comparison of dichloran 18% glycerol (DG18) agar with general purpose mycological media for enumerating food spoilage yeasts

Dichloran 18% glycerol (DG18) agar was originally developed to enumerate xe rophilic foodborne moulds. However, some laboratories are using DG18 agar a s a general medium to enumerate foodborne moulds and yeasts. A collaborativ e study, with the participation of seven laboratories, was undertaken to co mpare DG18 agar with dichloran rose bengal chloramphenicol (DRBC) agar, try ptone glucose yeast extract chloramphenicol (TGYC) agar, and plate count ag ar supplemented with chloramphenicol (PCAC) for enumerating 14 species of c ommon food spoilage yeasts. Comparison of the mean values of populations of all yeasts recovered on each medium revealed no significant differences am ong DRBC agar, PCAC, and TGYC agar, while each of these media supported the development of significantly (P < 0.05) higher numbers of colonies than DG 18 agar. However, differences were only 0.08 to 0.10 log(10) cfu/ml, making the practical significance questionable. The overall coefficient of variat ion (CV) for within laboratory repeatability was 1.71%, while the CV for re producibility of counts obtained among laboratories was 6.96%, Compared to DRBC agar, TGYC agar, and PCAC, yeast colonies were smaller on DG18 agar. G rowth of Brettanomyces anomalus, Cryptococcus albidus, and Rhodotorula muci laginosa was particularly retarded or inhibited on DG18 agar. Based on the performance of media in supporting colony development and ease of counting colonies, the use of DG18 agar as a general enumeration medium for foodborn e yeasts cannot be recommended. (C) 2001 Elsevier Science B,V. All rights r eserved.