Research Accomplishment Reports 2011

Rapid Assay, Probe Technologies, and Media for Monitoring Flora in Foodstuffs

C.L. Hicks
Department of Animal and Food Sciences

 

Non-Technical Summary

If rapid assays were developed that could be used in systems that contain some food solids, have high sensitivity, low preparation and assay time they would find immediate commercial application. A virtual nondestructive assay would have the greatest value in the marketplace. While there is zero tolerance for many pathogens in foods, usually enrichment methods are necessary to find these organisms using current assay procedures. Thus, if easy concentration methods were employed to collect bacteria from large samples, and an assay could measure 102 bacteria /ml or less and each assay costs less than $5.00 (including operator time), the rapid assay system would replace most other assays that require greater cost, greater preparation time, and higher skilled technicians.

One method being investigated is an Acoustic Emission (AE) assay, which appears to be specific for individual bacteria, including pathogens, that it can measure pathogens at a minimum concentration within a mixture of bacteria. This assay would have an initial up front cost for the equipment but the actual assay cost would be limited to operator time, a disposable sample vessel, and millipore filter, thus the actual cost may be far lower than most assays that are currently on the market. While this test would be considered a screening test, because it does not provide actual numbers of organisms present, it may be accurate enough to suggest contamination levels.

A second method being investigated is a rapid assay probe system that use bacteriophage peptide as a vector which is attached through a tether to a reporter molecule. While some commercial systems do use bacteriophage that have reporter molecules attached to them as rapid assay probes, this probe has the advantage of being much smaller, thus the number of probes that can saturate the host membrane goes up significantly, thus assay sensitivity increases with saturation. Also, once pathogen specific peptides from phage are characterized, highly specific peptides can be designed and synthesized to increase receptor binding and saturation. While this probe would be more expensive than AE assays, it may have some market application because of sensitivity. Again, this is a rapid screening technology and not a conformation technology.

Currently, companies pay identification laboratories from $19.00 (negative test) per assay for a standard plate assay that requires 7 days. ELISA tests cost about $25.00 per test and require 24 to 48 hours. PCR tests cost approximately $30.00 per test, take at least 12 hours, and are positive if dead cells are present. AE fingerprint assays would replace all PCR and ELISA tests (positive for non viable cells) currently being used by testing laboratories if assay times could be cut to 30 min because only viable cells numbers would be determined. Thus, several million assays/year would be performed for the food, regulatory, medical, and defense industries per year at a cost of greater than 120 million dollars per year (estimates derived from an average cost of $30/assay).