Comparative studies on the detection of salmonellae in milk and milk products using a horizontal (ISO 6785 : 2002) and a vertical (ISO 6785/IDF 93 : 2001) international standard

258 samples of raw milk, cheese (3 types) and dried milk products (2 types), 252 of which artificially contaminated with different salmonella serovars, were examined for salmonellae using the horizontal method ISO 6579:2002 Microbiology of Food and Animal Feeding Stuffs - Horizontal Method for the Detection of Salmonella spp. and the vertical method ISO 6785 / IDF 93:2001 Milk and milk products - Detection of Salmonella spp. With both standards the samples are preenriched in buffered peptone water and then transferred to Rappaport-Vassiliadis medium with soya peptone (RVS). The second liquid selective enrichment medium of ISO 6579:2002 is Muller-Kauffmann tetrathionate novobiocin broth (MKTTn), that of ISO 6785/IDF 93:2001 is selenite cystine medium (SC). RVS and SC (ISO 6785/IDF 93:2001) are incubated for 24 h and additionally 24 h before plating out onto brilliant green phenol red lactose sucrose agar (BPLS), RVS and MKTTn (ISO 6579:2002) are incubated only for 24 h before plating out onto xylose lysine deoxycholate agar (XLD). With both methods the second solid selective medium is free of choice. In the study presented here mannitol lysine crystal violet brilliant green agar (MLCB) and AES Salmonella agar plate (ASAP) were used. There were no differences between both methods if raw milk was used as sample material. However, with cheese and dried milk products the sensitivity of ISO 6579:2002 (90.2 % and 95.7 %, resp.) was lower than that of ISO 6785 / IDF 93:2001 (97.8 % and 100.0 %, resp.). In total RVS yielded 195, SC 185 and MKTTn 178 positive results. Depending on the type of food examined differences between the liquid selective enrichment media could be observed: In the case of raw milk SC showed the lowest recovery, in the case of cheese and dried milk products MKTTn yielded lower numbers of positive results than SC and RVS, and RVS was poorer than the other media when dried milk products were examined. In total with XLD less positive samples were found than with the other solid selective media. Plating out from MKTTn, however, the differences between XLD and BPLS were not striking.