Microbiology

PCR and ELISA methods, Nokes points out, are rather similar. It’s just the enrichment times that differ. “PCR has much fewer false positives than ELISA methods,” he adds. “With PCR, a positive is a positive. The FDA says show it, but our customers will take a positive PCR as a positive.” If you get a positive with an ELISA method, you have to validate it, he adds, and that means culturing in a Petri dish for several days.

While many food companies rely on PCR, in the eyes of federal regulators, a positive result using a DNA-based technology is “presumptive.”

The most popular tests among Microbac’s clientele, Nokes says, are E. coli and Salmonella and Listeria. “We can actually take that Listeria, find out the species and strain and track where it came from,” he adds.

The technology, he says, really shines when it is used to detect spoilage and monitor hygiene. The process applies PCR to the 16S gene reserve region that all bacteria have. A gel is then used to separate the amino acid to reveal the sequence.

“You don’t have to know what you’re looking for,” Nokes says. “You just know you have a problem and you learn what it is in two days as opposed to two or three weeks. Culture after culture after culture are just shots in the dark; but with this you can do fungal and yeast tests at the same time.”

But DNA testing isn’t always the best or only way, says Bruce Ritter, president and CEO of ELISA Technologies Inc., a Gainesville, Fla. maker of analytical test kits.

ELISA tests can detect specific protein targets like those that cause allergic responses. They are the best way to find and identify specific allergenic proteins in food, he says. For example, DNA tests can tell that it came from a cow, but cannot identify if it was from milk or meat.

“Every college teaches about genes and DNA, and that’s all well and good, but DNA tests cannot answer some of the questions that ELISA tests can,” Ritter says.

Immunoassays, he contends, are the tool of choice for detection of allergens in food because they can detect and identify the proteins that cause food allergies. As the list of allergens grows, he explains, there will be more tests developed for the allergenic markers.

“The ELISAs are faster, easier, more specific, more reliable and less expensive than DNA techniques,” he adds. “While everyone wants rocket science, sometimes all you need is a slingshot, and sometimes the simple answer is the best.”

Lock and Load Your Lab

The proving grounds, ultimately, are the laboratories, and a lab is only as good as its people and quality system, says Dr. Jeffrey L. Kornacki, president and senior technical director of Kornacki Food Safety Associates (Madison, Wis.).

Kornacki, who worked for several years as a microbiologist, now works as a consultant, and assists food companies with everything from sanitary facility and equipment design to lab quality systems to the good old fashioned microbiology basics.

“Product residue gets embedded and it’s almost impossible to clean,” says Jeffrey Kornacki. “The principles of sanitary design have been around for a long time. There needs to be a new cleaning and sanitizing paradigm that goes beyond throwing aqueous solutions on surfaces.”

Moreover, several types of food prep equipment apparently never had any design input from microbiologists.

“I was in a sandwich-making plant and the slicer part of a sandwich maker had 60 moving parts. How do you clean something like that? That’s a serious problem and it was designed by non-microbiologist,” Kornacki points out.