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Rapid detection of Listeria monocytogenes in food using culture enrichment combined with real-time PCR

O'Grady, Justin, Ruttledge, Margaret, Sedano-Balbás, Sara, Smith, Terry J., Barry, Thomas, Maher, Majella
Food microbiology 2009 v.26 no.1 pp. 4-7
foods, microbial detection, rapid methods, enrichment culture, polymerase chain reaction, Listeria monocytogenes, food pathogens, bacterial contamination, food contamination
A rapid method for the detection of Listeria monocytogenes in foods combining culture enrichment and real-time PCR was compared to the ISO 11290-1 standard method. The culture enrichment component of the rapid method is based on the ISO standard and includes 24 h incubation in half-Fraser broth, 4 h incubation in Fraser broth followed by DNA extraction and real-time PCR detection of the ssrA gene of L. monocytogenes. An internal amplification control, which is co-amplified with the same primers as the L. monocytogenes DNA, was also included in the assay. The method has a limit of detection of 1-5 CFU/25 g food sample and can be performed in 2 working days compared to up to 7 days for the ISO standard. A variety of food samples from retail outlets and food processing plants (n = 175) and controls (n = 31) were tested using rapid and conventional methods. The rapid method was 99.44% specific, 96.15% sensitive and 99.03% accurate when compared to the standard method. This method has the potential to be used as an alternative to the standard method for food quality assurance providing rapid detection of L. monocytogenes in food.