The search for best tools to detect pathogens

A decade has passed since the 2006 E. coli outbreak in spinach, and the world of produce processing has changed dramatically since that incident. A chain of events that has included the revision of the Food Safety Modernization Act (FSMA) and a series of other high-profile food safety outbreaks means that produce companies need to seek and destroy their tiny enemies.

“I see produce companies wanting to understand what’s in their fields, plants and packing houses,” said Lauretta Johnson, senior director of business development for Roka Bioscience. “The other big drivers are the end users – the retailers, Costcos and quick-serve restaurants are all pushing requirements back to the suppliers. There is collaboration between suppliers and retailers to make sure enough testing is being done to get a clear picture.”

These factors, plus the demands of FSMA that a company must prove its products are safe, change the approach from passive to active. Instead of waiting for the bad guys (the pathogens) to come to you, you have to put on your hunter orange (or a white lab coat) and go find them.

E. coli, listeria and salmonella are still the big three target pathogens. The methods used to detect their presence are changing. Traditional microbial testing technologies are labor intensive and too slow to be of maximum value in a situation where people are sick and the cause needs to be found quickly. Alternative technologies include lateral flow immunoassays, DNA-based tests that can check for multiple bacterial strains and whole genome sequencing. Produce processors are more likely to conduct traditional testing, immunoassay and DNA- based testing, whereas whole genome sequencing is more likely to be a tool of agencies such as the Centers for Disease Control and is used after an outbreak occurs.

When and where

Establishing a schedule for taking samples, particularly with swabbing, often starts with mapping out a facility and then determining the most logical times to take the samples.

At a recent Produce Marketing Association (PMA) webinar on microbial testing, Jim Gorny, vice president of food safety and technology for PMA, addressed the issue of synchronizing environmental swabbing with cleaning and sanitizing of equipment. Could the sanitizers interfere with test results? Gorny said testing should usually be done after sanitation and when the machinery has operated for two hours.

A microbial test involving enrichment, done in an Enrich 8 bag. Photo: Roka BioScience

“Listeria monocytogenes can work its way out of nooks, crannies and grooves,” he said. “If you sanitize and immediately test, there will be no listeria present. But if you run it midway through a shift, you might find it.”

Companies may also want to consider swabbing twice, said Peter Nielsen, technical director for Alliance Analytical Labs, Coopersville, Michigan.

“The first swab is after you clean and sanitize, to validate the effectiveness of your cleaning and sanitizing program. The second time is during operations, and that validates how effective your employee hygiene program is, including traffic control, cleanliness of the employees and cross- contamination during operations,” Nielsen said.

Another time to test, Johnson said, is after doing any physical reconfiguration of the equipment or the structure, including installation of new flooring or breaking through a wall. The environment should be tested to find out if the work caused any pathogens to break free from their hiding places.

Microbial testing could conceivably take place at any location along the field-to-fork chain of custody, but some places are more logical than others. At the PMA webinar, Trevor Suslow, food safety research specialist with University of California Extension, said testing of seed and soil is a rare occurrence. Testing of soil amendments is standard if the materials are coming from a certified supplier. Irrigation water testing is uncommon, but increasing. Preharvest product testing is variable and increasing with many commodities.

Preharvest testing can be valuable to get a snapshot of the field as birds and mammals encroach into the growing environment. Testing immediately after harvest can be a good idea, especially if a company wants to take the safe approach and assume pathogens are present from field conditions.

“Once the crop gets into the cooling facility and the packing houses, environmental testing definitely needs to be strong and to even include in-process product testing,” Johnson said. “You’re making sure that what’s coming into the plant is clean and that the environment is clean the whole time it’s there.”

As the FSMA final rules have rolled out, there has been plenty of discussion and speculation about the efficacy of finished product testing.

“Testing at the shipping point is variable, but there’s lots of evidence that it is increasing, particularly over the last year and six or seven months. Finished product testing at the product receiver is uncommon, but increasing,” Suslow said.

Tests of the finished product may be something to consider for a produce company because the government and buyers are either conducting them or wanting to see last-minute spot checks. One logical place to test is just before the product goes into a bag or other type of package.

On the other hand, waiting to test until the finished product stage may be too late to yield the most useful information or to prevent a problem.

“Finish product testing doesn’t tell you if the problem is in the raw material or the food contact surface,” Gorny said. “But if you do test, have a plan for positives. I can’t tell you how many folks say they have a positive but don’t know what to do about it.”

Finding the right lab

When selecting a third-party laboratory to conduct microbial testing and evaluation, consider these questions:

  • Does the lab have experience with produce? Tell the lab workers and leaders that you grow or process a specific kind of fruit or vegetable and ask them how they would handle sampling and testing for that crop. The lab staff should be able to say that they have validated that commodity and then be able to tell you how it is tested.
  • Is the lab certified and its processes validated? There are a number of auditing and certification bodies, including PrimusLabs, ISO, AOAC and SQF. These kinds of certifications help ensure the quality of the test result.
  • Have you visited the lab? “You don’t have to be a microbiologist or an expert, but you can walk in and see if it’s clean and well-managed. Do people look like they know what they’re doing? Is there a chain of custody? Is there someone there to greet you? You will get a feeling for these things if you do a little bit of due diligence,” Johnson said.

There’s another option: don’t use an outside lab and do testing in-house. There may be economic reasons to do this, but there is also a risk factor involved with having pathogens so close to the product.

“The best practice is to not have it within the facility,” Nielsen said. “In one case, the lab was external to the facility, but technicians were still going back and forth, and they carried it (the pathogen) in with them. Out of curiosity, we went into the lab and did swabbing and the pathogen was everywhere. These folks were doing the best that they could do, but there’s something about being qualified. With these microorganisms, you have to be careful.”

Lee Dean, editorial director

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