Rapid Micro Rolls On

Editor’s Note: This article on the history and impact of advances in rapid food microbiology is the second in a new series for Food Quality. In “FoodTech: Tools That Changed the Industry,” we look at various technologies and tools, such as rapid microbiological testing, that have played a key role in and had an indelible impact on the food industry.

In the science fiction series “Star Trek,” science officer Spock would merely point his tricorder at the surface of a new planet to instantly determine its composition and potential for human inhabitation. The medical version of the device could swiftly diagnose an illness in a Starfleet officer. While this holy grail of real-time testing has yet to be realized in today’s food and pharmaceutical industries, new and improved tools are moving toward that goal.

The MagMAX Express is designed for labs that perform high-throughput pathogen detection tests. When used with the PrepSEQ Nucleic Acid Extraction Kit, this instrument offers an automated way to prepare bacterial DNA using magnetic beads.

“We are on the leading edge of PCR (polymerase chain reaction) detection by now,” said Morgan Wallace, PhD, senior research microbiologist at DuPont Qualicon, Wilmington, Del. “It’s not yet a tricorder” in terms of immediate response, he added.

DuPont and other companies are racing to improve test responsiveness, both in turnaround speed and sensitivity. Part of the impetus is the heightened public awareness of food safety that followed notorious pathogen contaminations, some involving peanut butter and ground beef, which sickened and killed many people. Companies are not only sensitive about their corporate reputation but are also mindful of the huge amount of money required for recalls or for products stored in warehouses awaiting results from slow-growing cultures.

“The public health case is driving food microbiology now,” said Donald Zink, PhD, senior science advisor to the U.S. Food and Drug Administration’s Center for Food Safety and Applied Nutrition. Zink said rapid methods have progressed more slowly than expected, as sample-size preparations and amplification remain impediments to speedy results.

“It is critical to get enough of a pathogen to detect and also to determine whether the organisms are dead or alive,” he said. “We have yet to get away from some type of amplification.” He estimates cultured methods, either broth or agar, still account for more than 50% of testing, primarily because of the low cost.

Purnendu Vasavada, PhD, food safety and microbiology specialist at the University of Wisconsin in River Falls and a member of the Food Quality editorial advisory board, is more optimistic. “We’re pretty close to real-time testing.” With biosensors and other new technologies, it could happen in two to five years, he said.

Philippe Gadal, PhD, CEO of AES Chemunex, a company that offers Scan RDI, BactiFlow ALS, and D-Count products for food testing, said that even though Petri dishes remain the broad-based, basic tool for general testing, future biochips will test for multiple pathogens.

Mike Doyle, PhD, director of the University of Georgia’s Center for Food Safety, expects new technology to revolutionize the field. He pointed to ribosomal RNA, which can produce more copies than DNA. “There are more targets for molecular testing, and you don’t have to go through an extensive enrichment process,” Dr. Doyle said.

Microbiology testing volume has grown 17.8% since 2005, from 629.9 million to 738.3 million tests, said Tom Weschler, MBA, founder of Strategic Consulting Inc., in Woodstock, Vt. The total market for food microbiological testing surpassed $2 billion in 2008. “Food companies want to sell safe products, but they also want to protect their brand name,” he said.

Attention to pathogens is paying off. The overall incidence of E.coli O157:H7 has declined 42% since 1996, according to a report by the Centers for Disease Control and Prevention and others. The data also showed substantial declines in Campylobacter, Salmonella, and Yersinia that were attributed to enhanced surveillance and outbreak investigations.

Image of results from 1995 using polymerase chain reaction with gel-based detection, with band placement readings for 8 tests in one batch

Faster and Easier

Because the enrichment step is time-consuming, companies are taking steps to reduce that time. DuPont, for example, reduced amplification and detection of E. coli to less than one hour on its PCR-based BAX product, a significant reduction compared to the 3.5 hours needed with earlier machines. After enriching E. coli for about eight hours, the company saved time by taking a measurement at the end of each PCR cycle instead of at the end of every batch. The system is closed tube instead of gel-based to simplify the process, Dr. Wallace said, so that people with less training can perform the assay, and the results are better. The company has 13 PCR assays that target nine microbes. BAX can detect multiple species at the same time in one PCR reaction.