Large-volume immunomagnetic separation combined with multiplex PCR assay for simultaneous detection of Listeria monocytogenes and Listeria ivanovii in lettuce

Multiplex polymerase chain reaction (mPCR) has been widely used for the simultaneous detection of various target bacteria in vegetables. However, an enrichment period is necessary to improve the sensitivity of the mPCR method. In this paper, large-volume (10 mL) immunomagnetic separation (IMS) combined with mPCR for the rapid detection of Listeria monocytogenes and Listeria ivanovii in lettuce without further enrichment process is reported for the first time. Various parameters that affected the capture efficiency (CE) of IMS, including the amounts of streptavidin and biotinylated anti-Listeria monoclonal antibodies on the surface of magnetic nanobeads, the amount of immunomagnetic beads, immunoreaction time, and magnetic separation time, were systematically investigated. Moreover, the concentrations of primers, PCR conditions, and genomic DNA isolation for mPCR assay were optimized. Under optimum conditions, the CE of large-volume IMS for L. monocytogenes and L. ivanovii was greater than 90% when the concentration of target bacteria was less than 106 CFU/mL in pure culture, and was more than 80% when the concentration was below 105 CFU/mL in lettuce samples. The limit of detection of IMS combined with mPCR assay reached as low as 1.0 CFU/mL in pure culture and 10 CFU/g in lettuce. The overall assay time, including sample preparation, large-volume IMS, and mPCR assay, took less than 7 h. In summary, the developed large-volume IMS-based mPCR system exhibits great potential for routine screening detection of foodborne pathogenic bacteria for safety monitoring. (C) 2015 Elsevier Ltd. All rights reserved.