Back in the 1970s, cop shows like “S.W.A.T.” would sometimes refer to the bulletproof vests that police officers wore. These days, you don’t hear much about bulletproof vests—now they’re called body armor or bullet-resistant vests because none of them are completely bulletproof. Tom Weschler feels the same way about the term “rapid microbiology” when it comes to pathogen detection. “Most of the current systems really aren’t that rapid,” said Weschler, president and founder of Strategic Consulting Inc., a leading diagnostic test consultant. “They may be more rapid than systems we’ve had in the past, but they’re certainly nowhere near real time.”
Explore this issueAugust/September 2009
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That is a problem for the food industry, which has gotten a series of black eyes from recent nationwide and multistate outbreaks involving Salmonella in peanut butter, spinach, and tomatoes, Escherichia coli O157:H7 in beef and spinach, and Listeria in deli meats. With new food safety legislation likely to pass Congress soon, inspections and other food safety activities will increase, and the urgent need for truly real-time methods for foodborne pathogen detection will also increase. “The longer it takes to get test results in, the more product you have to put on hold and store until you get the results,” said Michael Doyle, PhD, Regents Professor of food microbiology and director of the Center for Food Safety at the University of Georgia.
Two Current Pathogen Detection Tools
Currently, the more rapid microbiology tools for pathogen detection generally involve one of two options: antibody-based immunoassay or genetic amplification using real-time polymerase chain reaction (PCR). With both methods, time to result has shrunk exponentially compared with previous approaches, which often took from three days to a week to yield results.
For example, DuPont Qualicon’s BAX System Q7 now offers a reverse-transcriptase PCR assay that can detect Listeria in eight hours—the first commercial application of RNA technology to foodborne pathogen detection. This technique does not require the usual full enrichment step; instead, Listeria cells are resuscitated by heating in the collection buffer solution for four hours.
The company is now developing a BAX assay for E. coli O157:H7 that will drive time to result down to nine hours by shortening cycling time. “We’ve eliminated the post-cycling detection step by detecting signal at the end of each cycle and re-optimized the cycling conditions to shorten each cycle,” said George Tice, DuPont Qualicon’s director of research and development.
Another goal is greater integration, Tice said. “We’d like to be able to integrate at least sample prep and amplification detection, so that a customer could put on a sample, walk away, and come back and get the result. Of course, we have to be able to do that at a price that’s acceptable to the market.”
BioMérieux recently announced a new immunoassay in its VIDAS pathogen detection line, VIDAS UP (ultimate performance) for the detection of E. coli O157:H7. The company, which has a big presence in Europe, is extending its market in the U.S. Instead of using an antigen-antibody reaction to capture the bacteria, it uses a phage protein.
“We’re not actually working with bacteriophage per se, but the tip of the filaments that come off the phage that attach to the bacteria,” said J. Stan Bailey, PhD, director of scientific affairs for industrial diagnostics at bioMérieux. “From a German company that has been working on this technology for more than 10 years, we’ve licensed the protein materials on the tip of those fibers, which we use as a capture on the immunoassay. This allows us to have much better specificity, no cross-reactivity, and a very tight binding.”
For meat, produce, and irrigation water products, VIDAS UP has a seven-hour time to result with smaller sample sizes (around 25 grams), eight hours for larger sample sizes, and 10 hours for large pool samples.