Table 1 : Percentage of positive samples found in the different culture media.

1. Salmonella isolation: comparison of different enrichment mediaE.V. De Bussera, J. Dewulfa, K. Houfa, D. Maesa , L. De ZutteraaFaculty of Veterinary Medicine, Ghent University, Belgiumemily.debusser@ugent.be 1. Introduction Different media and culture methods are available for the isolation of Salmonella. The present study aimed to assess the effect of different culture media on the amount of Salmonella contaminated samples that could be detected and on the Salmonella serotypes that could be isolated. The enrichment media used in this study were: Rappaport-Vassiliadis (RV) broth, Rappaport-Vassiliadis Soya (RVS) broth, Diagnostic semi-solid Salmonella (DIA) agar, Simple Method Salmonella (SMS) agar, Modified Semisolid Rappaport-Vassiliadis (MSRV) agar and Mueller Kauffmann Tetrathionatenovobiocin (MKTTn) broth. Serotyping of 29 of the 74 isolates revealed the presence of SalmonellaTyphimurium in 51.7% (15/29), followed by S. Derby (24.1%) and S.Infantis (3.4%). In 20.7% (6/29) of the samples different seroytpes were found. 2. Materials and Methods The duodenal content of 458 pigs belonging to randomly chosen batches at different Belgian slaughterhouses was collected and submitted to Salmonella isolation according to the following steps. Ten grams of feces was diluted 1:9 with buffered peptone water (BPW) and incubated at 37°C. After 16-20h, 0.1 ml of the BPW culture was added to 10 ml RV and 10 ml of RVS, spotted on DIA, SMS and MSRV. Finally, 1 ml of the BPW culture was added to 10 ml MKTTn . After incubation for 24h at 42°C (except MKTTn at 37°C), the DIA, SMS and MSRV plates were examined for the presence of migration zones. A loopful of the edge of the migration zones and of each RV, RVS and MKTTn enrichment broth was streaked on a Xylose Lysine Desoxycholate (XLD) agar plate. After incubation for 24 h at 37°C, all XLD plates were examined for the presence of typical colonies. Isolates were first tested biochemically, followed by genotyping in an enterobacterial repetitive intergenic consensus (ERIC) PCR (1). Representatives of each genotype were selected for serotyping in the Belgian reference laboratory (Veterinary and Agrochemical Research Centre, Ukkel, Belgium). 4. Discussion In this study, the semi-solid enrichment media (MSRV, DIA, SMS) were able to detect the highest amount of contaminated samples. The fluid media (RV, RVS, MKTTn) showed much lower results. The combination MSRV, RVS and MKTTn was able to detect 94.4% of all positive samples. Furthermore, in the samples serotyped until now, different serotypes could be detected in 20.7% of the positive samples and this between the different media used, but also within one medium. Differences between the media are probably due to an asynchronous growth among serotypes in certain selective enrichment (2). Recovering different serotypes from one medium can be explained by the migration capacity of the different Salmonella serotypes. These results indicate that the use of multiple media is efficient in the detection of more contaminated samples and in the demonstration of different serotypes that could be found in one sample. Regarding epidemiological studies this should be kept in mind and diagnostic methods should be improved. Table 1: Percentage of positive samples found in the different culture media. 3. Results The results show that in 15.5% (71/458) of the sampled pigs Salmonella could be isolated from the duodenal content in at least one of the used techniques. In Table 1 the number of positive samples found by each culture media are shown. 5. References 1. RasschaertG., et al. (2005). Comparison of five repetitive sequence based PCR typing methods for molecular discrimination of Salmonella enterica isolates. J. Clin. Microbiol. 43, 3615-3623 2. Rostagno MH, et al. (2005). Culture methods differ on the isolation of Salmonellaenterica serotypes from naturally contaminated swine fecal samples. J. Vet. Diagn. Invest. 17, 80-83