Highly sensitive and rapid biosensor slated for testing.

Scientists at the Georgia Institute of Technology (Georgia Tech Research Institute, EOEML, Room 223, Baker Building, Atlanta, GA 30332) plan to test a biosensor that can simultaneously identify bacterial species and determine concentrations of multiple pathogens-including E. coli O157:H7 and Salmonella-in foods. The sensor is able to determine contamination in products in less than 2 hr when operating on the processing floor.

The most significant advantage of the biosensor is the time saved in assessing the presence of contamination. Most companies perform laboratory tests, but they are costly and slow, sometimes not even yielding results for 48 hr to 72 hr. That delay requires that food products remain stored in warehouses for longer periods.

The new sensor would minimize the chance of final product contamination. Georgia Tech researchers and colleagues have been developing and testing the biosensor in their lab for about four years. Now they are ready for a field test expected to start this November at Gold Kist Inc. (Carrollton, GA). Laboratory tests have proven the biosensor is highly sensitive, able to detect pathogens at minute levels of 500 cells/ml. Researchers believe they can improve that sensitivity to 100 cells/ml. Current laboratory methods only achieve sensitivity levels of 5000 cells/ml, and they usually take from 8 to 24 hr to yield results. In addition, lab equipment costs $12,000 to $20,000 per instrument, compared with an estimated $1000 to $5000 for a biosensor.

But before the biosensor gains market acceptance, it must prove its effectiveness in the upcoming field test. The first phase will last three to six months, and researchers will be comparing their results with the company's lab findings. Researchers will examine the reproducibility of results. They will split a sample for testing using the biosensor and lab tests. For every 1000 tests they do, they will look for any variations among results.

The biosensor can simultaneously detect 12 different pathogens, but researchers are concentrating on six bacterial species for now. They are Salmonella, E. coli O157:H7, generic E. coli, L. monocytogenes, C. jejuni and Y. enterocolitica. The biosensor operates using integrated optics, immunoassay techniques and surface chemistry. It indirectly detects pathogens by combining immunoassays with a chemical sensing scheme.

In the immunoassay, a series of antibodies selectively recognize target bacteria. The capture antibody is bound to the biosensor and captures the target bacteria as it passes nearby. A set of reporter antibodies, which bind with the same target pathogen, contain the enzyme urease, which breaks down urea that is then added and produces ammonia. The chemical sensor detects the ammonia, affecting the optical properties of the sensor and signaling changes in transmitted laser light. These changes reveal both the presence and concentration of specific pathogens in a sample at extremely minute levels.

The field test is expected to demonstrate the biosensor's ability to improve food processors' operations, but it has some competition from other techniques. One under development is an electrochemical technique that can reportedly detect pathogens at 100 to 1000 cells/ml.

Further information. Nile Hartman; phone: [phone]; fax: [phone]; email: [e-mail].