Improved detection of Listeria monocytogenes in soft mould-ripened cheese

In comparison with standard methods, enrichment in half-Fraser broth for 24 h at 30 degrees C, followed by plating out onto Listeria monocytogenes blo od agar (LMBA) and PALCAM medium combined with an additional streak proved to be the most rapid and specific method for the detection of indigenous L. monocytogenes populations from soft mould-ripened cheese, This procedure, with a high sensitivity (93%) and a low detection limit (1-10 cfu 25 g(-1)) , provided negative and presumptive positive results within 2-3 d. Differen ces between LMBA, PALCAM and Oxford medium turned out to be highly signific ant (at 99% significance level); plating on LMBA after standard enrichment protocols giving the best overall results, An improvement in detection was also obtained by modifying the confirmation procedure. A loopful of culture (an additional streak) from PALCAM or Oxford medium was streaked on non-se lective medium in addition to streaking only separate colonies as specified in the standards.