Browsing by Subject "Milk products"

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    Entwicklung und Validierung schneller und selektiver Verfahren zum Nachweis von Salmonella enterica, Cronobacter spp. und Bacillus cereus in Milcherzeugnissen
    (2014) Zimmermann, Jennifer; Schmidt, Herbert
    The presence of pathogens is a serious problem in the food industry and contaminations of food with Bacillus cereus, Cronobacter spp. and Salmonella enterica are responsible for a large number of diseases worldwide. Milk products like milk, whey or cream powder are widely used in industry as an ingredient in other foods. Therefore it requires a fast and reliable identification of pathogenic microorganisms. The official methods according to § 64 LFGB or ISO/TS 22964 apply a common scheme of pre-enrichment, selective enrichment, detection and confirmation and take between three and six days. The aim of this work was the development and validation of a real-time PCR based method, which identifies the existence of the three pathogens in dairy products within 24 hours. The identification of B. cereus, Cronobacter spp. and S. enterica with the developed TaqMan real-time PCR was performed using specific genetic characteristics and an internal amplification control to eliminate false negative results. For B. cereus, the groEL gene, which codes for a heat shock protein, was selected as target. For the detection of Cronobacter spp. the ompA gene and for S. enterica the invA gene was chosen. Both genes are responsible for the invasion of the pathogens in the human epithelial cells. The adaptation of the method to the food matrix and an optimization of the enrichment time were affected by an artificial contamination of various dry dairy products. It was possible to detect 105 cfu/g C. sakazakii and S. Enteritidis cells with an initial concentration of 100 cfu/g in reconstituted powdered infant formula after enrichment of six hours. To simulate a natural contamination, powdered infant formula was contaminated with desiccated C. sakazakii cells in various concentrations and analyzed with the developed real-time PCR method. It was possible to detect an inoculum concentration of 0.01 CFU/g dry stressed C. sakazakii cells at low aw values (0.22). The new TaqMan real-time PCR is fast, reliable and specific for the clearly detection of the three major pathogenic microorganisms in milk products and was carried out within 24 hours.