Fighting Against Food Pathogens

Because FoodNet collects data from public health departments in 10 states, representing only 15 percent of the U.S. population, the nationwide numbers are much larger. Additionally, the actual number of foodborne illnesses always exceeds the number reported because many people who get sick do not seek, or necessarily require, medical treatment.

Not only does the FoodNet report “provide important information about which foodborne germs are making people sick in the United States,” says Robert Tauxe, MD, director of CDC’s Division of Foodborne, Waterborne, and Environmental Diseases, but “it also points out changes in the ways clinicians are testing for foodborne illness and gaps in information as a result.”

In particular, FoodNet counts infections diagnosed both by traditional, culture-based methods as well as those diagnosed using newer, culture-independent diagnostic tests (CIDTs). CIDTs, such as
immunoassays and nucleic-acid amplified tests, can be faster and easier than traditional culture-based methods, which also require use of trained personnel. CIDTs can identify a general bacteria type within hours without having to culture, or grow the pure bacteria strain (or isolate) in a laboratory, a process that typically takes days.

But without the isolate, public health scientists are unable determine the DNA subtype (“fingerprint”), its resistance pattern, or other characteristics necessary to detect outbreaks, track antibiotic resistance, monitor disease trends, and ultimately prevent outbreaks, CDC says.

For instance, PulseNet, the CDC-run network that connects public health and food regulatory agency laboratories, relies on the collection of DNA fingerprints of bacteria taken from sick patients to identify local and multistate outbreaks. The growing use of CIDTs is endangering PulseNet’s effectiveness. “Without a DNA fingerprint of the bacteria, CDC and public health labs will not be able to find, monitor, and prevent foodborne disease outbreaks, track antibiotic resistance, or follow trends to know if prevention policies are working,” CDC says.

Problems with Culturing

Regulatory bodies in both U.S. and the European Union are emphasizing the reduction of Campylobacter and Salmonella while increasing testing requirements, says Mike Clark, International PCR group manager, Food Science Division, Bio-Rad Laboratories. “Industry must be equipped to respond to these changes with testing solutions that are fit-for-purpose,” he tells Food Quality & Safety.

PCR techniques are based on amplification of the DNA of target pathogens. As the cost and complexity of genetic testing began to come down in the 1980s, PCR became commonplace in government and in company labs. Today, it remains among the most widely used approaches to detecting foodborne bacteria.

But because PCR also requires culturing, identification can still take many days. Advanced PCR tests, including quantitative and real-time PCR, can produce results more quickly by using probes and primers designed to target highly-conserved regions of the target genome.

“Many laboratories are using conventional methods combined with molecular methods for detecting these two foodborne pathogens,” Dr. Narvaez explains. For example, PCR is often combined with immunomagnetic separation that uses antibody-antigen interactions to detect very low levels of pathogens. “These are probably among the most-used methods used by industry and academia, and are approved by regulatory agencies,” she explains.

However, even these are not fast enough because they can take upwards of 24 hours, including enrichment, to produce definitive results. “Scientists are working on developing detection methods that can be sensitive and specific but also faster, ideally less than one hour with no enrichment, to obtain definitive results,” Dr. Narvaez says.

New Technologies and Approaches

Among the many developments in laboratory and onsite testing are advances in established approaches such as time-of-flight mass spectrometry; the invention of novel biosensors and assays using bacteriophages, enzymes, antibodies, nucleic acids, cell receptors, or polymers; nanotechnology-based sensors; and other rapid detection methods. The following are summaries of a few of these approaches.