Improving the Detection of Foodborne Pathogens

Since the Jack-in-the-Box outbreak in 1993, food contamination continues to dominate the headlines. On June 28, a Colorado meat company agreed to expand a recall of beef due to possible contamination with the bacteria E. coli 0157.H7. Both the company and the U.S. Department of Agriculture (USDA) said that the beef may be linked to illness in at least 18 people.

Recently, a Chicago meatpacker was forced to recall 6,152 pounds of ground beef products that may also have been contaminated with E. coli O157:H7. In addition, a Portland, Oregon meat distributor had to recall 39,973 pounds of ground beef products that also appeared to be contaminated with the same type of bacteria.

Food contamination cases aren’t limited to meat and poultry, either. FDA inspectors “visiting” facilities as part of a follow-up audit on last spring’s widespread pistachio recall (due to the presence of the disease-causing bacteria Salmonella), discovered the possibility that contaminated nuts may have been repacked and distributed to airports and hotels. And on June 19, Nestle USA announced that it was voluntarily recalling its Toll House refrigerated cookie dough products after a number of people became sick after eating the raw dough.

Since the Nestle cookie dough story broke, CNN has reported that 25 people have been hospitalized, and seven have developed hemolytic uremic syndrome, a type of kidney failure associated with E. coli O157:H7. Federal microbiologists are sorting through Nestle’s Danville, Va. plant, which produces the refrigerated cookie dough, to begin the detective work necessary to find the source of the potentially deadly strain of the bacterium.

“The key here is the phrase ‘detective work,’” says leading expert in high pressure bioscience and biotechnology, Dr. Edmund Ting, senior vice president of South Easton, Mass.-based Pressure BioSciences, Inc., who has spent years researching the effects of high hydrostatic pressure on pathogens that contaminate the food supply, such as E. coli, Listeria, and Salmonella. Ting believes that improvements in food safety depend on the rapid and accurate detection of foodborne pathogens, both in pre-release quality control testing and in post-outbreak investigations. Such detection depends to a great extent on the quality of the extraction of the DNA, RNA, and proteins (“biomolecules”) from the pathogens contaminating the food.

“Current extraction methods rely principally on heat, electrical charge, sonication, homogenation, and chemical partitioning, all of which can alter and sometimes even destroy sensitive and important biomolecules (such as proteins), or fail to liberate them from complex biological structures,” explains Ting. “Consequently, it may be difficult to find the contaminating pathogen if the sample preparation method cannot reproducibly and effectively extract or identify the pathogen’s biomolecules from the food sample prior to testing.”

New sample preparation technologies continue to be developed, enabling scientists to extract biomolecules related to food-borne pathogens more quickly, accurately, and efficiently than ever before. One example cited by Ting, pressure cycling technology (PCT), employs cycles of hydrostatic pressure between ambient and ultra-high levels (up to 35,000 psi and greater) to safely, reproducibly, and efficiently release DNA, RNA, and proteins from food, plant, and biological samples within minutes, allowing for more rapid and accurate downstream testing.

At present, PCT technology is being used by approximately seventy-five laboratories around the world, mostly in the areas of biomarker discovery (to detect markers for cancer, stroke, neurological disease, etc.), soil and plant biology (to detect pathogens harmful to food crops, such as wheat and strawberries), forensics (mostly in the detection of DNA), human disease (to detect microbes that live on or in the human body), and counter-bioterror applications. Currently, several USDA laboratories are employing the technology, as is at least one laboratory of the Food and Drug Administration (FDA).

Ting believes that the issues affecting the quality of sample preparation in the food safety industry are fundamentally the same as those facing the biotech drug discovery and development laboratory. Traditional sample preparation methods are difficult to reproduce due to user variability, sample collection contamination, and the fundamental process limitations of the basic extraction technology. Conversely, PCT uses pressure, a bio-physical force that is instantaneously and uniformly transmitted to all points within the disposable sample container, thus offering the potential to standardize the sample preparation process, a significant advantage to any method.

“Current sample preparation methods used in the food industry may fail to preserve sensitive and important biomolecules, especially proteins, or fail to liberate them from complex biological structures,” explains Ting. “It may be difficult to effectively find the contaminating pathogen if the sample preparation method cannot reproducibly and effectively provide proper preparation of the sample, in order to efficiently release pathogen DNA, RNA, or proteins from the food sample prior to testing and analysis.”

The food safety spectrum involves not only bacteria pathogens but also allergens and genetically modified organism (GMO) issues. “All of these areas will depend on effective sample preparation methods,” said Ting. “Having speed, increased reproducibility, the opportunity for greater accuracy, and the ability to standardize the preparation of the samples to be tested, will better allow for “hold and release” strategies, which should further enhance food safety.”

“Higher levels of quality are now being expected from the food industry and the scientific community to develop better ways to increase the safety of the world’s food supply,” says Ting. “To that end, we believe that new sample preparation methods, such as PCT, will begin to play more important roles in the identification of foodborne pathogens going forward.”