Validation of a Diagnostic PCR Method for Routine Analysis of Salmonella spp. in Animal Feed Samples
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Validation of a Diagnostic PCR Method for Routine Analysis of Salmonella spp. in Animal Feed Samples Charlotta Löfström & Charlotta Engdahl Axelsson & Peter Rådström
Received: 20 August 2007 / Accepted: 28 September 2007 / Published online: 29 December 2007 # Springer Science + Business Media, LLC 2007
Abstract As a part of a validation study, a comparative study of a PCR method and the standard culture-based method NMKL-71, for detection of Salmonella, was performed according to the validation protocol from the Nordic validation organ for validation of alternative microbiological methods (NordVal) on 250 artificially or naturally contaminated animal feed samples. The PCR method is based on culture enrichment in buffered peptone water followed by PCR using the DNA polymerase Tth and an internal amplification control. No significant difference was found between the two methods. The relative accuracy, relative sensitivity and relative specificity were found to be 96.0, 97.3, and 98.8%, respectively. PCR inhibition was observed for rape seed samples. For the acidified feed samples, more Salmonella-positive samples were found with the PCR method compared to the NMKL method. This study focuses on the growing demand for validated diagnostic PCR methods for routine analysis of animal feed and food samples to assure safety in the food production chain. Keywords Animal Feed . NordVal . Salmonella . Validation . PCR . Polymerase Chain Reaction
C. Löfström : P. Rådström (*) Applied Microbiology, Lund Institute of Technology, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden e-mail: [email protected] C. Löfström : C. E. Axelsson Lantmännen AnalyCen AB, P.O. Box 905, SE-531 19 Lidköping, Sweden
Introduction Food-borne diseases such as salmonellosis are recognized as one of the most serious public health concerns today (Tirado and Schmidt 2001). The problem of salmonellosis related to the food industry is cyclic, and animal feed may serve as a reservoir for Salmonella contributing to the spread of the bacteria along the food chain (Davies and Hinton 2000). The conventional culture method used today for detection of Salmonella in feed is laborious and takes 3–7 days to complete (Anonymous 1999). Hence, there is a growing demand for rapid methods for the detection of Salmonella in feed samples. Polymerase chain reaction (PCR) is considered to be one of the most promising techniques to meet this demand, and several PCR-based detection methods for Salmonella in food and feed have been developed (Hoorfar et al. 2000; Salomonsson et al. 2005; Löfström et al. 2004; Malorny et al. 2003a, 2004). Although the PCR-based methods meet the demands of diagnostic laboratories on detection methods regarding sensitivity, specificity, and ease of use, the introduction of the technique for diagnostic use has so far been slow. The technological novelty of the technique, the high investment cost, and the lack of officially approved, validated, and standardized methods have been mentioned as reasons for this delay (Malorny et al. 2003a,
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