Rapid Detection of Listeria in Dairy Products
Dr. Bart C. Weimer, Utah State University
Dr. Marie Walsh, Utah State University
Listeria monocytogenes is a pathogenic microbe that causes serious illnesses and even death. Each year, the bacteria cause at least 2,493 cases of listeriosis. Of these, 2,298 persons are hospitalized and 499 persons die. The case fatality rate is high, i.e. 20 deaths per 100 cases of illness. Although HACCP and GMP are increasingly common in food industry companies, product recalls because of the chance of contamination are still the case. Listeria monocytogenes remains the primary agent in those recalls (25 out of 55 in 1999). This information and the fact that this organism grows well at refrigeration temperatures, suggest that a rapid detection technique for Listeria monocytogenes in food is needed.
A 2-stage test will be created. A preliminary (presumptive) result will be generated quickly (15 minutes). If the presumptive test is positive, the sample will be further processed to extract the DNA from the cells on the bead surface. This will be used in a PCR reaction to confirm the presumptive result and differentiate L monocytogenes from other species. The combined use of the ImmunoFlow system and PCR allows a presumptive and confirmed diagnostic test in a rapid (30 minutes) and sensitive format (~100 cells). The easy use of the system will also be a big advantage.
The basis of this system involves the use of a patented flow-through capture cartridge that binds the pathogen onto the surface for subsequent detection. In the cartridge, a flow through fluidized bed module containing large (3 mm) glass beads was created. The glass beads are coated with covalently-bound antibodies against Listeria. By pumping contaminated samples through the bed, bacterial cells are captured and concentrated on the beads. This lead to three advantages:
1) Larger sample volumes of milk can be tested.
2) No pre-enrichment step is needed.
3) Lower amounts of Listeria monocytogenes in food samples is concentrated on the beads for detection.
4) The presumptive step is automated.
5) Subsequent verification with PCR is done in an inhibitor-free environment.
Wim Lippens - in progress