Efforts to Improve Rapid Microbiology Tools

“These nanorods allow us to increase the Raman signal that’s emitted by whatever pathogen we’re looking at by 100-million fold — basically, 1018 detection, at the sub-atomic level,” said Ralph Tripp, PhD, professor and Georgia Research Alliance Chair of Animal Health Vaccine Development at the College of Veterinary Medicine at the University of Georgia. “This means that we don’t have to modify the pathogen, do any form of amplification, or even go through extraction. We can just detect it in a specimen.”

To date, the majority of Dr. Tripp’s work has been with the Department of Defense and the Centers for Disease Control and Prevention, detecting bacteria and viruses such as respiratory viruses and HIV. But Dr. Tripp and the company he founded to advance the SERS pathogen detection technology, Argent Diagnostics Inc., are also leveraging it within the food industry, working with the U.S. Department of Agriculture on the detection of Salmonella, Listeria, and E. coli.

Molecular Fingerprinting in 60 Seconds

“We can do molecular fingerprinting on meat and poultry using SERS within 60 seconds,” Dr. Tripp said. “We usually use about two microliters of analyte for detection, but it’s possible to use one microliter or less.” Argent is now commercializing the technology in a biosensing unit for water baths in the poultry industry. Although it has mostly been studied in meat and poultry, Dr. Tripp does not foresee any major challenges to adapting the SERS technology for use in produce pathogen detection.

Compared to real-time PCR and immunoassay, the technology is not particularly expensive. “Essentially, we’re taking microscope slides and growing silver nanorods on them, and the cost for that can range between $1 and $3 a slide. On each slide you can do 36 individual analyses, so it’s very cost-effective,” Dr. Tripp said. “The instrument cost is essentially that of a confocal microscope—between $8,000 and $30,000, depending on whether you get the Cadillac version or not. We’re now building a lower-cost instrument specifically for the food industry to detect substrates.”

Tools like these may soon herald the end of PCR and immunoassay in food industry pathogen detection. “They’ve served us well and are the best we have right now, but they’ll be history in a couple of years,” Dr. Doyle said.

He points to recent outbreaks, such as the listeriosis outbreak in deli meats in Canada that killed 22 people. “Had they been testing end products for Listeria monocytogenes, they would have found it. When the testing of contaminated product was done, some not even by food testing companies, they were finding it in unopened samples. The same with the PCA peanut butter problem and other such outbreaks—if they had been testing finished products for pathogens, they likely would have identified the problem before the outbreak and could have taken corrective action.”

Truly real-time pathogen detection methods would make that much more feasible. “If companies aren’t volunteering to do more end-product testing, they will be forced into it either by regulators or the legal system, and in order to do this practically and economically, they’re going to have to have these shortened tests,” Dr. Doyle said. “Having assays that can give results in a matter of minutes will be real advantages both for industry and the consumer, and I don’t think it’s that far off. Right now, industry’s more interested than ever, and federal agencies certainly are as well.”

Shaw is a freelance writer based in Montclair, N.J. Reach her at [email protected].