Dr. Shu Chen from the University of Guelph (Canada) presented this afternoon at the Annual North American Summit on Food Safety, describing her work on developing molecular methods for food safety and quality monitoring. There are several molecular methods for genotyping food pathogens and tracing them back to their source. These include:
- Amplified Fragment Length Polymorphism (AFLP); and,
- Multiple Locus Variable Number Tandem Repeat Analysis (MVLA).
Examples of AFLP applications are the PCR-based BAX (Dupont) and Assurance GDS (BioControl) detection platforms. AFLP works much like RFLP, except that, following digestion of the DNA sample with restriction enzymes, the sticky ends of the resulting fragments are ligated (attached) to adapter sequences and specific combinations of adaptor-fragment sequences are then targeted by the PCR primers. The use of the adaptors adds sensitivity to the test. The BAX system detects Listeria spp., Salmonella spp. and E. coli O157:H7 with high sensitivity and allows the user to run one test for all species. Assurance GDS is a highly sensitive system with three levels of specificity beginning with an immunomagnetic separation (IMS) procedure, to isolate bacteria from the sample, followed by PCR using highly specific primers and a patented probe. IMS uses antibody-coated magnetic particles that are specific to the target organisms, E. coli O157:H7 and Salmonella spp.