Detection of L. monocytogenes in enrichment cultures by immunoseparation and immunosensors

There is a need to identify the presence of bacterial pathogens in foods earlier than it is currently carried out. At present, pre-enrichment culture followed by selective agar plating are standard microbiological methods applied to detect Listeria monocytogenes and other bacterial pathogens with zero tolerance in food products. PCR and biosensor methods may shorten the time required to individuate contamination by L. monocytogenes in a pre-enrichment culture. In this study, a protein chip immunosensor with a sensitivity of 100 bacteria/ml was developed for Listeria spp. detection. The method provides a 10 fold increase in sensitivity compared to published work on bacteria immunosensing coupled to fluorescence detection. When 40 ml of Listeria spp. pre-enrichment culture were processed by immunoseparation, the limit of detection (LOD) was lowered to 2.5 cfu/ml. The results were confirmed by a qPCR method whose sensitivity was of 0.1 cfu/ml. The method based on immunosensors combined with immunomagnetic separation (IMS) on pre-enrichment cultures may shorten the time required for species identification. We also showed the potential for multiplexing of the protein chip method demonstrating the selective detection of Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli, and Campylobacter spp. A future development is the integration into a system for rapid screening of pathogens contaminating food productions.