Submitted to: Molecular and Cellular Probes
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/23/2003
Publication Date: 10/15/2003
Citation: Fratamico, P.M. 2003. Comparison of culture, polymerase chain reaction (pcr), taqman salmonella, and transia card salmonella assays for detection of salmonella spp. in naturally-contaminated ground chicken, ground turkey, and ground beef. Molecular and Cellular Probes. 17(5):215-221. Interpretive Summary: Salmonella, a major food-borne pathogenic bacterium, causes an estimated 1.3 million cases of food-borne illness and 553 deaths each year in the United States. Due to the relatively high prevalence of Salmonella in meat and poultry products, rapid, sensitive, and reliable methods for detection of this bacterium in foods are needed to reduce the occurrence of salmonellosis caused by consumption of contaminated foods. To address this need, four types of assays were evaluated for detection of Salmonella in naturally-contaminated retail ground chicken, ground turkey, and ground beef. These included methods based on: (1) culturing food enrichments onto selective agar growth media; (2) two types of assays based on DNA amplification using the polymerase chain reaction (PCR); and (3) an antibody-based assay (immunoassay). There was good agreement between the results of the culture and the PCR methods; however, agreement between the results of the immunoassay and the other methods was poor to fair due to the occurrence of false positive results using the immunoassay. Results of the PCR assays showed that 35.5% (61/172), 28.5% (60/208), and 6.5% (7/108) separate samples of the ground chicken, ground turkey, and ground beef were positive for the presence of Salmonella. In summary, results of this study indicate that PCR-based methods are sensitive and specific and can be used to monitor for the presence of Salmonella in foods.
Technical Abstract: Four types of assays were evaluated for detection of Salmonella spp. in retail ground chicken (86 packages), ground turkey (104 packages), and ground beef (54 packages). Two 25-g samples from each package were separately subjected to pre-enrichment in buffered peptone water for 20 h at 37ºC followed by enrichment in Rappaport Vassiliadis (RV) broth for 20 h at 42ºC. The RV enrichments were diluted and plated using a Spiral Plater onto Rambach agar, Rainbow Agar Salmonella, and XLT4 agar. The RV enrichments (1 ml) were also subjected to DNA extraction using the PrepMan reagent and tested by a PCR assay targeting the Salmonella invA gene, as well as by the TaqMan® Salmonella assay. Additionally, 1 ml of the RV enrichment was heated at 100ºC for 20 min and tested using the Transia Card Salmonella® immunoassay. Results showed that 16.8, 24.0, 28.8, and 26.4% of turkey samples were positive for Salmonella spp. by culture, PCR, TaqMan PCR, and Transia Card Salmonella assays, respectively. Eighteen, 28.5, 35.5, and 34.9% of chicken samples were positive by culture, PCR, TaqMan PCR, and Transia Card Salmonella assays, respectively, and 6.5, 6.5, 6.5, and 18.5% of ground beef samples were positive by the four assays, respectively. Analyses of the data using the kappa statistic showed that there was substantial to excellent agreement between the PCR and TaqMan PCR assays and between the PCR and culture assays (kappa coefficients ranging from 0.67 to 0.87), while there was poor to fair agreement between the results of the Transia Card Salmonella assay and the other methods (kappa coefficients ranging from 0.28 to 0.32). Overall, results showed that the PCR-based assays were more sensitive than the culture method, and the culture and PCR-based assays were more specific than the immunoassay for detection of Salmonella in ground chicken, turkey, and beef due to the occurrence of false positive results using the immunoassay.