Journal of Applied Microbiology, Vol.116, No.1, 167-178, 2014
Evaluation of pre-PCR processing approaches for enumeration of Salmonella enterica in naturally contaminated animal feed
AimsThree pre-PCR processing strategies for the detection and/or quantification of Salmonella in naturally contaminated soya bean meal were evaluated. Methods and ResultsMethods included: (i) flotation-qPCR [enumeration of intact Salmonella cells prior to quantitative PCR (qPCR)], (ii) MPN-PCR (modified most probable number method combined with qPCR) and (iii) qualitative culture enrichment PCR. The limit of quantification was 18x10(2)CFUg(-1) (flotation-qPCR) and 002MPNg(-1) (MPN-PCR). Fifteen naturally contaminated Salmonella positive soya bean meal samples from one lot were analysed in parallel with the three methods, using 25, 50 and 25g of feed, respectively, resulting in detection of Salmonella in 6, 15 and 9 bags. Enumeration resulted in 18x10(2)-78x10(3)CFUg(-1) (flotation-qPCR) and 0024 to >52MPNg(-1) (MPN-PCR). ConclusionsExcept for differences in methodology, results obtained with the three techniques could be due to the presence of nonculturable Salmonella and/or a heterogeneous distribution of Salmonella in the material. Significance and Impact of the StudyThe evaluated methods provide different possibilities to assess the prevalence of Salmonella in feed, together with the numbers of culturable, as well as nonculturable cells, and can be applied to generate data to allow more accurate quantitative microbial risk assessment for Salmonella in the feed chain.
Keywords:animal feed;buoyant density;flotation;food safety;most probable number;PCR-MPN;quantitative PCR;Salmonella