The ABCs of Microbial Testing

April 27, 2021
Processors who need microbial testing have a lot of options, including doing it themselves.

In the food and beverage industry, it’s often the small things that get you. And they don’t come any smaller than microorganisms.

Microbial contamination is the second-leading cause of FDA product recalls, behind undeclared allergens. They lead to high-profile recalls and worse, with devastating and even crippling consequences for processors.

Keeping track of pathogens and other microbes is one of the most vital safety-related tasks in any food processing plant. The means of doing so vary, according to individual requirements and resources. The basic questions are: What is being looked for, how, and by whom?

Arguably the most fundamental decision about microbial testing is whether to have it done by a third party or to do it onsite. Third-party labs are the more accessible option for smaller operations. Perhaps their biggest advantage is ease of use; the processor just ships samples, swabs, etc., off to be tested.

This isn’t just a matter of convenience. Many processors are leery of handling pathogenic samples in the same facility where they make food, especially with tests that require growing microorganism colonies. Another advantage is that third-party labs are usually run to rigid standards and often have access to expertise.

“We boast some of the most knowledgeable scientists in the laboratory industry and are represented on many of the top food safety and quality assurance committees as technical and guidance experts,” says Sue Ann Seitz, director of sales for Food Safety Net Services.

Third-party testing also involves less initial expense, since users don’t have to invest in equipment or even testing components, which are usually furnished by the lab. In addition, there is no need to set aside a secure space for an onsite lab.

Petrifilm readers can easily scan the results of 3M’s Petrifilm disposable samples and keep track of trends.

On the other hand, operational expenses for third-party testing can be daunting. “Food processors can spend hundreds of thousands of dollars per year sending out samples to reference labs for micro testing,” says Annie Lundquist, professional service representative at 3M. “If they bring that testing in-house, they perform it internally for a fraction of that cost. By reducing their cost per test, it enables them to increase their testing frequencies or sample volume without breaking the bank.”

Another significant disadvantage to third-party testing is time. Typically, product loads have to be held up until they’re cleared by the tests, which, if done by third parties, take 48 to 72 hours to turn around. In-house testing can often be done in 24 hours or less.

Bringing it inside

In-house testing has the advantages of versatility and speed. It also costs less on an ongoing basis, once the initial investment has been made.

On the other hand, that initial investment can be steep. Processors who want to do their own testing must not only buy the equipment but set aside space for a laboratory/testing area to do it. This space must be secure enough to prevent cross-contamination, which means isolation, adequate ventilation, entryways that can be secured and other factors.

Training is another factor. Employees must be trained to collect samples, either from product or from environmental swabs on surfaces. In addition, protocols must usually be put in place to prevent cross-contamination. These usually involve restricting access to the lab in some way. Options include requiring a badge or key code for entry, using unique colors for coats to be worn in the lab and having doors that can only open at the top, to ensure that samples are handed off without unauthorized persons actually entering the lab.

Lundquist recommends that these conditions be in place for in-house testing: a dedicated lab space with proper ventilation, employees to run the lab and a budget for their salary, proper biohazard waste disposal and enough testing volume to make it all cost-effective.

Test subjects

There are two basic types of microbiological testing. One looks at “indicator organisms,” such as total coliforms, staphylococcus, and yeast and mold. The mere presence of these organisms is not evidence of contamination – in fact, having some of them around is inevitable. But when the plate count of indicator organisms starts to mount, it’s indicative of a potential problem.

One of the biggest challenges involved in indicator organism testing is where to set the baseline – the limits on total plate count. That’s something that usually has to be established through data history.

“By understanding how many organisms are considered normal in a sample, we can develop specs for that sample,” Lundquist says. Petrifilm is 3M’s flexible, disposable, ready-to-use testing plate; users simply deposit a drop of sample between the top and bottom film, let it incubate and count the colonies of indicator organisms. 3M’s Petrifilm readers can not only speed up the counting process but keep track of trends to help set baselines for individual products.

“Petrifilm is used to understand bacteria or yeast and mold in your product that is considered normal, develop a spec or a threshold and then monitor that product based on that spec going forward,” Lundquist says. “By tracking these results over time, we can also understand trends and identify the cause of contamination.” These could include spikes during certain seasons or even certain days, for causes that could include inadequate sanitation, insufficient lethality of a kill step or contamination of raw ingredients.

The other basic type of microbiological testing looks for specific pathogens, like E.coli O157:H7 or salmonella. Finding these, Lundquist says, is like looking for the proverbial needle. The samples must be put in a culture medium that will grow the pathogens, if they’re present, to the point where they’re detectable. That procedure is more hazardous than taking plate count samples, to the point where many food processors shy away from it.

“For food safety, the first thing is you don’t want to be growing pathogens anywhere near a food processing facility,” says Ted Andrew, vice president of sales and marketing for Certified Laboratories. For this reason, some companies will do their total plate counts in-house but send out pathogen testing.

The Gene-Up from BioMérieux uses polymerase chain reaction to detect specific pathogens.

More sophisticated pathogen-testing methods are available that have faster time to result than most traditional methods but are just as sensitive and accurate. Immunoassay methods do this by searching for antibodies associated with specific pathogens. Gene-based methods, the most common of which is polymerase chain reaction (PCR), search out and automatically multiply strands of DNA belonging to pathogens, to the point where they can be detected.

Processors who opt for these kinds of pathogen detection methods can choose from a variety of self-contained systems. PerkinElmer, for instance, markets the Solus line, which includes all required culture media, labware, application-specific assay kits and automated workstations, and can offer results in 48 hours (or 24 hours for the Solus One system). 

BioMérieux markets the Gene-Up, a PCR system that comes with a wide array of test kits for common pathogens like salmonella and listeria, as well as customized solutions for unique applications.

3M has the Molecular Detection System, which uses loop-mediated isothermal amplification (LAMP), a gene-based alternative to PCR that it touts as more robust, efficient, sensitive and specific.

Of course, when it comes to pathogens, there’s no ignoring one of the most consequential and dangerous of all: SARS-CoV-2, the virus that causes COVID-19. However, it’s not a pathogen that affects food safety in the same way as the microbes, most of them bacteria, that microbiological tests are set up for. There have been no verified cases of its being transmitted through food or packaging, it doesn’t live for long on surfaces and the most overwhelmingly common method of infection is through the air.

Third-party labs often have expertise that is not available with in-house testing. Photo: Food Safety Net Services

Nonetheless, some companies are offering tests and assays for SARS-CoV-2 in environmental swabs. And they say the pandemic is altering demand for food safety testing.

“Throughout the pandemic, we have seen fluctuations in a variety of industries, some increasing and some decreasing at various times,” says Seitz of Food Safety Net Services. “Now that COVID vaccinations are becoming more prevalent, many of the industries are now stabilizing and increasing their food safety testing protocols.”

One of the biggest effects of the pandemic on the food industry was a disruption in production schedules caused by shifts in demand. That affected microbiological testing along with everything else, says Joy Dell’Aringa, scientific marketing manager for BioMérieux.

“Testing plans often correlate to production runs and volumes, so while some testing volumes have decreased for market segments affected early on in the pandemic, others have continued to hold steady or increase based on new consumer demand and product innovation,” Dell’Aringa says.

Andrew says Certified Laboratories’ business hasn’t changed all that much in the pandemic. Some of the larger customers, he says, already had in-house labs but decided to move to third-party testing temporarily, to handle overflows. There also was an increase in startup food processors, who tend to need more support and guidance, he says.

Microbial safety is a daunting responsibility, with many options available. Food processors must make the basic decision about in-house or third-party testing, and then seek help to evaluate available alternatives for safe, cost effective and productive microbiology testing.

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