Friday, August 17, 2007

Food Pathogen Detection



Contaminated food has been in the news a great deal lately. These incidents expose the obvious need need for testing food samples for the presence of many different, harmful bacteria in a single, fast, affordable test.

The common laboratory tool called a microarray, commercially available at www.arrayit.com can address this need in a more cost effective and high throughput manner than any other device. Like a microprocessor in a computer, microarrays multiplex, miniaturize and parallelize the analysis of many sample types. Unlike existing testing assays, no time consuming and expensive culturing of bacteria is necessary for accurate testing. As the name suggests, microarrays can be setup as an "array of arrays" of tiny spots (500 picoliters each) of many thousands of different test sites across many different samples. These microarray biosensors are manufactured with a special robots commercially called the NanoPrint and SpotBot microarrayers. Many of these robots are in use all over the world. In the case of food pathogen testing, the array of tiny spots contain bacteria recognition elements (typically proteins or DNA) which can bind to complimentary bacteria or bacterial components from food samples. Sometimes these same devices are referred to as biochips or biosensors.

Andrew Gehring and his colleagues in a lab at the USDA built a prototype system and published their results in their paper titled, Protein-Based Microarray for the Detection of Pathogenic Bacteria.

Gehring, A.G., Albin, D.M. 2007. Protein-Based Microarray for the Detection of Pathogenic Bacteria. Journal of Rapid Methods and Automation in Microbiology. 15:49-66

As a prototype system, they developed an antibody-based protein microarray and demonstrated that it could detect in tact Escherichia coli (E. coli) O157:H7 cells. E. coli O157:H7 is a harmful bacterium that is responsible for numerous outbreaks of food borne illness, and even death, in the United States every year.

Specifically, the test first captured E. coli O157:H7 with an antibody that was attached to a microarray. The microarray was made with a SpotBot microarrayer. Then, a second antibody with a fluorescent marker was detected and measured with a laser scanner was used to determine if any E. coli O157:H7 were captured. In this research, the microarray approach was optimized in several ways to facilitate rapid detection of intact bacterial cells. In the future, microarray-based tests will be used by all regulatory agencies as well as food producers to rapidly assess for the presence of multiple, harmful bacteria in numerous food samples.