A comparison of standard cultural methods for the detection of foodborne Salmonella species including three new chromogenic plating media.

In this study the draft of the horizontal method for the detection of Salmonella species from human food and animal feed (ISO 6579:2002) was compared to the European gold standard (DIN EN 12824:1998), including the three new chromogenic plating media AES Salmonella Agar Plate (ASAP), Oxoid Salmonella Chromogen Media (OSCM) and Miller-Mallinson agar (MM). First the growth and appearance of 36 bacterial type strains (Salmonella and other 21 species) on ASAP, OSCM and MM were compared to those on the three traditional agars Brilliant Green Agar according to Edel and Kampelmacher (BGA), Xylose Lysine Deoxycholate Agar (XLD) and Xylose Lysine Tergitol 4 Agar (XLT4). Only on MM agar, did all of 36 tested type strains produce typical colonies, especially strains of S. Senftenberg, Salmonella arizonae, S. Dublin and S. Derby. Artificial inoculation experiments using raw pork ground meat (n=92) were subsequently conducted. A shortened incubation time of 24 h in RVS broth yielded a Salmonella species recovery of 100% from spiked meat samples. Finally, 286 naturally contaminated raw porcine and bovine minced meat samples and raw poultry meat samples were investigated. Forty-three strains from a total of 39 Salmonella-positive samples were found. S. Typhimurium (n=21), with DT 104 L, DT 012 and RDNC being the most prevalent subtypes isolated. D-tartrate-positive S. Paratyphi B (n=2) and S. Saint-Paul (n=3) were also recovered. They were cultured from poultry meat and were multi-resistant against antibiotics including nalidixic acid. Rappaport Vassiliadis broth with soypeptone (RVS) yielded the highest recovery of Salmonella spp. (97,4%) compared to Tetrathionate broth with Novobiocin according to Muller and Kauffman (MKTTn, 94,9%) and Selenite Cystine broth (SC, 38,5%). However, no significant difference was obtained by comparing the ISO 6579:2002 draft to the gold standard.