Comparison of the ISO and IDF methods for detection of Listeria monocytogenes in blue veined cheese

The International Dairy Federation Revised Provisional IDF Standard 143:1990 (1990) is compared with the ISO Draft International Standard ISO/DIS 11290-1 (1995) for detection of Listeria monocytogenes in inoculated samples of the blue veined cheeses Gorgonzola and Adelost (Swedish blue mould cheese) and in non-inoculated market cheeses of mostly soft mould cheese. The ISO method detected L. monocytogenes significantly more frequently than the IDF method when inoculated Gorgonzola samples were analysed. For inoculated Adelost, and non-inoculated market cheeses the methods were equally good. The selective isolation media PALCAM and Oxford Listeria selective agar, were compared for recovery of Listeria spp. Less growth of non-Listeria colonies was obtained on PALCAM agar compared to Oxford Listeria selective agar especially after the primary enrichment step of the ISO method. Consequently, it was easier to identify and isolate growth of Listeria species from the cheeses on the PALCAM agar.