Detection of viable and dead Listeria monocytogenes on gouda-like cheeses by real-time PCR |
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Authors: | Rudi K Naterstad K Drømtorp S M Holo H |
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Institution: | MATFORSK, Norwegian Food Research Institute, Osloveien, As, Norway. knut.rudi@matforsk.no |
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Abstract: | AIMS: Surface contamination by Listeria monocytogenes of gouda-like cheeses during processing represents a potential public health problem. The aim of this work was to develop novel real-time PCR diagnostics to detect the presence of viable, dead or viable but not culturable (VBNC) cells on gouda-like cheeses. METHODS AND RESULTS: We used ethidium monoazide bromide (EMA)-PCR for direct quantification of viable and dead cells, while semiquantitative detection of culturable cells below the PCR detection limit (c. 100 CFU g(-1)) was obtained by combining growth and real-time PCR. We were able to quantify the fraction of >0.5% viable cells in a background of dead cells by EMA-PCR, given that the viable cell concentration was above the PCR detection limit. The combined growth and real-time PCR complemented the EMA-PCR, and enabled semiquantitative detection of low levels of culturable cells (10 and 100 CFU g(-1)). SIGNIFICANCE AND IMPACT OF THE STUDY: The significance of this work is that we have developed a novel concept for detection of viable and potentially infectious L. monocytogenes. |
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Keywords: | DNA diagnostics ethidium monoazide bromide Listeria monocytogenes real-time PCR viable but not culturable viable/dead diagnostics |
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