Tag Archives: microbiology

Joy Dell'Aringa, bioMerieux

Proficiency Testing Considerations

By Joy Dell’Aringa
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Joy Dell'Aringa, bioMerieux

Proficiency testing has increased in food microbiology laboratories in response to various factors: ISO 17025 accreditation increases, regulatory focus, customer requirements, internal quality requirements and an increase in validation and verification activities. Here we will explore available resources, testing considerations, and response guidance for participating food microbiology laboratories.

What is Proficiency Testing?

Proficiency testing (PT) is widely used in the food testing industry as a way to verify that an individual laboratory is capable of performing a given method. There are several ISO 17043-accredited PT providers that issue unknown samples with various organisms and matrices throughout the year. Heather Jordan, director of LGC PT operations for the API Group in North America, says the increase in participating labs has led to additional insights on the value of PT programs. “We receive feedback from participants that they also find gaps in their methods and operations as a result of the PT. For example, a participating laboratory recently uncovered a reagent expiry system flaw that impacted results and implemented improvements. Another laboratory reported that they were experiencing challenges with a unique matrix type – and through the PT process identified the issue and validated the process adjustments made.” Participating laboratories report analytical results to the PT provider and evaluations are issued based on statistical success criteria. Additionally, performance is often reported to third party entities defined by the laboratory, such as ISO 17025 accreditation bodies and other certifying authorities.

Considerations When Designing a Proficiency Testing Plan

ISO 17025-accredited laboratories are required to have a written proficiency testing plan. Operations not bound by accreditation requirements are still encouraged to document their PT plan as a matter of best practice. When designing a PT plan, laboratories should consider the following:

  • Proficiency Provider(s)

    • Selecting a PT provider is the first step in designing a PT program. Providers may be evaluated based on available accreditation status, analytes and matrices, frequency, data deliverable, accreditation status and cost.
    • Common Microbiology PT providers include:
      • LGC / American Proficiency Institute (API)
      • AOAC
      • Various Regulatory Bodies
    • ISO 17043 is the international standard that proficiency providers are accredited to by various accrediting bodies. When evaluating a PT provider, you should ensure that they are accredited to this standard. A list of ISO 17043 accredited PT providers can be found here: https://portal.a2la.org/pt/PT_Summary1.pdf
  • Matrix & Analytes

    • Matrices selected should be representative of the matrices routinely tested by the microbiology laboratory. Common matrices available include: Dehydrated Mashed Potatoes, Non-Fat-Dry-Milk (NFDM), Powdered Cooked Beef (PCB) and Environmental. The laboratory should consider not only the category of matrix, but also constituency. For example, a dairy laboratory would likely select the NFDM matrix. However, a laboratory that analyzes primarily animal proteins may select the PCB, even if they do not analyze beef specifically.
    • PT providers offer several target analytes for laboratories to choose from. Laboratories should incorporate the appropriate PT’s into their PT plan that match the routine and/or critical analytical operation of the laboratory. Most PT providers will offer package combinations of various quantitative and qualitative tests that include key pathogens and indicator organisms of interest. Laboratories can also select to add on analytes that might be more specialized to their operation such as Campylobacter , STEC or Lactic Acid Bacteria.
  • Frequency:

    • Each PT provider offers scheduled PT rounds throughout the year. When creating the PT plan, the laboratory should consider how often they will participate. Factors to consider are often third party requirements, risk and cost. Often customers or third party certifying bodies will specify a minimum frequency of testing. In the absence of a predefined frequency, laboratories should weigh the risk of failure vs. cost and resources to determine the best frequency. For example, if a laboratory fails a PT- how long before the next PT round is received can be critical to the corrective action process. Many providers will offer off-schedule rounds to aid in troubleshooting and corrective action investigations. Quarterly and biannual frequency is quite common. Annual participation is often the minimum requirement, however many operations find that is not frequent enough to meet PT plan objectives and goals.
  • Rotational Models to Consider

    • Laboratories that conduct multiple methods for the same analyte and/or have several analysts will often incorporate a rotational model in the proficiency testing plan. PT events often have a limited amount of sample to process, which can also create a logistic challenge. A rotational plan is flexible and custom to each operation, but essentially ensures that each method and analyst is evaluated at least annually via PT programs. A rotational plan should also consider how to conduct PTs in order to capture routine operational conditions including staffing, capacity and workflow conditions of the laboratory.

My PT Samples Arrived! Now What?

Once the PT samples have arrived, having a predetermined plan will aide greatly in efficient and organized processing and analysis. Laboratories often designate an individual as a “PT Coordinator” that will schedule the testing event and notify pertinent administrative and lab personnel prior to the arrival of the samples. This helps to ensure all testing reagents and consumables are available and that the needed personnel are available on the days required. The PT Coordinator can organize any rotational aspects of the PT plan, report results, monitor deadlines, receive results and initiate the corrective action process if needed.

PT samples should be prepared according to PT provider instructions so that the laboratory has a working sample to test. This is a critical step and, if not done properly, can have a significant impact on the results. To ensure comparable results across participants the PT provider may include important details in the instructions such as what dilution level to consider the prepared sample, or what characteristics must be present to consider the sample a positive. The working sample should be treated the same as a ‘real world’ sample that would be received by the laboratory. Activities such as sample login, entry into a LIMS or SAP system and set up are important to follow as the laboratory would routinely.

Once the laboratory is in the sample preparation and analysis portion of the PT, it is important to avoid any method modifications unless the laboratory routinely performs a validated modification for a given method. Remember, the PT event is designed to verify the laboratories ability to perform a method, therefore, all factors of sample receipt, set up, analysis and reporting, should be incorporated into the PT process.

When the analysis is complete and results are available, the PT Coordinator can report them to the PT provider. Be mindful of making proper calculations, proper categorical results and appropriate confirmations. Report all results just as the laboratory typically reports them. For example, if the laboratory routinely reports Yeast & Mold as a combined count, or if Listeria is routinely confirmed to the species level, be sure to report it in the same manner for PTs. Records generated through the PT event should also follow the same recording and record keeping process in accordance with laboratory policies. To ensure that records are robust enough for potential troubleshooting, take great care in documenting any anomalies of the event.

Reporting and Response

In addition to reporting results externally to the PT provider, who may also report to other external organizations at the laboratories discretion, the laboratory may also have an internal reporting structure. Once the results are received from the PT provider indicating success or failure for each parameter, the laboratory may also share these results internally, especially if there are multiple laboratories within the network.

If an unsatisfactory result is reported, the laboratory should implement a pre-determined corrective action process. Often this will include several parties such as the lab manager, analysts, PT coordinator and a QA representative. Heather Jordan reminds us that an unsatisfactory result isn’t necessarily a failure for the laboratory. “We encourage laboratories to ask themselves the question ‘was this testing scenario relevant to my operation?’ If not, then they should document accordingly.” For example, a laboratory’s standard practice might be to fail a product on specification if an indicator organism count was too high (such as generic E. coli) and therefore they would not test the product further for a targeted pathogen. In this case, they should document how their laboratory would have handled a similar real life sample according to their procedures and store that documentation with their PT results. The laboratory may even proactively communicate this investigation to their accrediting body. The investigation of an unsatisfactory result should include a document and record review, interviews with participating parties, discussion with other network laboratories (if applicable), and communication with outside stakeholders such as accrediting bodies, the PT provider and the diagnostic company for the corresponding method (if applicable). Often the PT provider will provide educational commentary or guidance on a sample that can also be useful in a corrective action investigation. Many times laboratories will request troubleshooting samples from the same round as the unsatisfactory result – not necessarily to negate the original results – but to aide in the root case and corrective action process.

Newer Regulations Clarify Food Microbiology Parameters for Labs

By Jacob Bowland
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Accuracy and validity of food test results hinge on purified water and annual water testing.

Laboratory-grade water literature is well documented among the large life science water manufacturers. General levels of resistivity, total organic carbon (TOC), particles and bacteria in water classify into Types 1, 2, or 3, with Type 1 having the most stringent requirements. Each type is useful for a different application depending on the procedure:1,2,3

  • Type 3. Generic applications where water will not come into contact with analytes during the procedure
  • Type 2. Standard applications such as media and buffers
  • Type 1. Critical applications such as GC, MS, HPLC analyzers4

Achieving high-quality water requires purification through a polishing step such as deionization (DI), reverse osmosis (RO), ultraviolet light (UV), filtration or distillation, which removes specific impurities.3,5

This classification system gets muddled, as different agencies have their own standard that examines different end-point analysis and levels:

  • ISO (International Organization for Standards)
  • CLSI (Clinical and Laboratory Standards Institute)
  • ASTM (American Society for Testing & Materials)
  • USP (United States Pharmacopoeia)2,5

With all these standards and testing in place, many labs assume that their installed DI water supply is clean, yet in reality, the water in general would be closer to Type 3 rather than the required Type 1. 

The problem with using lower quality water in food testing labs is that the accuracy and validity of tests will be compromised. Many of the analyzers requiring Type 1 water would recognize contamination from lower quality water, creating difficulty in identifying actual contamination or yielding false positives. False positives can result due to microorganism contamination in the water that is amplified through the testing procedure. In addition, dirty water can damage expensive machinery, because tools in the laboratory that are designed for a high-purity water supply can malfunction when less-pure water is used. For example, a system with microfilters can become rapidly clogged with lower quality water, introducing the possibility of flooding when tubing bursts, if left unnoticed.

Newer regulations in regards to ISO 11133:2014, along with ISO 17025:2005, provide clarity on food microbiology water parameters for the laboratory. ISO 11133:2014 “Microbiology of food, animal feed and water–Preparation, production, storage and performance testing of culture media” describes how water for culture media must be purified. The purification recommended is distilled, demineralized, DI, or RO, and stored in an inert container. To verify purity, labs must regularly test the water to assure microbial contamination is kept to a minimum. Regarding 17025:2005, which refers to food microbiology requirements for accreditation, there should be daily, weekly and monthly testing of the laboratory’s water source to verify required quality for microbiological water. Daily testing examines resistivity of water; monthly testing examines the water’s chlorine levels and aerobic plate counts; yearly testing examines heavy metals in the water. Therefore, accuracy and validity of food test results critically revolve around producing purified water and annual water testing.

1. Veolia. (n.d.). Water Quality. Retrieved from: http://www.elgalabwater.com/water-quality-en-us
2. Puretec Industrial Water. (n.d.). Laboratory Water Quality Standards. Retrieved from: http://puretecwater.com/laboratory-water-quality-standards.html
3. Millipore. (n.d.). Water in the Laboratory. Retrieved from: http://www.emdmillipore.com/US/en/water-purification/learning-centers/tutorial/OPab.qB.IxUAAAE_MkoRHe3J,nav
4. Denoncourt, J. (2010). Pure Water. Retrieved from: http://www.labmanager.com/lab-design-and-furnishings/2010/09/pure-water?fw1pk=2#.VRrT7fnF-Cn
 5. The National Institutes of Health. (2013). Laboratory Water, It’s Importance and Application. Retrieved from: http://orf.od.nih.gov/PoliciesAndGuidelines/Documents/DTR%20White%20Papers/Laboratory%20Water-Its%20Importance%20and%20Application-March-2013_508.pdf

Jacob Bowland is Product Manager at Heateflex and Steven Hausle is Vice President of Sales and Marketing at Heateflex.


Thomas R. Weschler, Founder and President, Strategic Consulting, Inc (SCI)

Faster, Better, Cheaper… What’s Most Important in a Pathogen Test?

By Thomas R. Weschler
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Thomas R. Weschler, Founder and President, Strategic Consulting, Inc (SCI)


For close to 20 years, Strategic Consulting Inc. (SCI) has been following the industrial microbiology market, and food safety testing applications in particular. As part of the data gathering for our most recent report, Industrial Microbiology Market Review, SCI interviewed 15 senior managers at major food companies and food contract labs (FCLs) to understand their priorities when choosing a pathogen diagnostic method. The interviews were roughly split between food companies and food contract labs.

SCI identified ten important attributes for evaluating a diagnostic method or instrument, and asked the interviewees to stack rank the top five items most important to them.

The three top-ranked choices were the same at both food companies and FCLs, with sensitivity/specificity the most important attribute. Second in importance was the ability of the method to be utilized in a broad range of food matrices. Ranking third was the cost-per-test for diagnostic reagents.

For food companies, time-to-results (TTR) was tied for third in the stack ranking, followed by ease-of-use (EOU)/automation in fifth place. Clearly food companies want quick results but only after they are assured that the pathogen diagnostic they are using provides accurate results and is able to work with a range of food types.

For food contract labs, the cost of the pathogen diagnostic instrument ranks fourth, and TTR is tied with the cost of labor per test for fifth. For FCLs, most of the key attributes in method selection are based on operational considerations, which makes perfect sense given testing is their business.

Sangita Viswanathan, Former Editor-in-Chief, FoodSafetyTech

Using Microbiology Studies to Support your Product

By Sangita Viswanathan
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Sangita Viswanathan, Former Editor-in-Chief, FoodSafetyTech

What is a Special Project? These are special testing projects that are not typically covered by laboratory testing when you run into a question that you really can’t answer, says Centrella. Special projects can be used for:

  • Development, validation or implementation of a new testing method;
  • Comparing performance of a new testing platform against a standard;
  • Validation of pathogen control, for instance, to check effectiveness of CCPs;
  • Shelf-life investigation;
  • Verification of effectiveness of antimicrobials; and
  • Determination of whether a product requires refrigeration.

With method validation, the situation can be that you work with PCR for Salmonella, and there are certain number of matrices approved, but you want to take advantage of that method and extend the matrix. So special projects can help you answer if that method would be suitable for your product.

Another category of special projects is pathogen control. In this situation, you can see if you have a process or an ingredient that’s in your product, or simulate that intervention in a lab setting (either heat or cool step or a treatment like a wash) to check for pathogen growth. In this case, the target matrix is inoculated with high level of analyte, and the aim is to show large log reduction, or even complete elimination, once the matrix is treated with the intervention.

Shelf-life studies is another example of special projects. In this case, we simulate retail storage of the product to determine expected shelf life or determine typical storage conditions. Here, assay are prepared to assess threats to product shelf-life, microbial, chemical or nutritional in nature. Such threats could be build-up of lactic acid due to bacterial activity, or might be gas-producing microorganisms, or chemical targets that cause rancidity in oils. Often these include an organoleptic compound which could change how a product looks, or if it has an odor. It’s important to remember that often the souring of the product due to lactic acid, gas bubbles or off odors will present themselves before microbial counts become obvious.

Shelf life testing is conducted at predetermined intervals, and depending on need, we can stagger these intervals, for instance, we can do more frequent testing during the anticipated end of shelf life. The final shelf life is defined by the last acceptable result.

Antimicrobial effectiveness is another example of special projects, and these involve products that already have an antimicrobial ingredient. In these situations, we inoculate target microorganism into the product and use assay to determine log reduction, or prevention of outgrowth. Antimicrobial effectiveness studies often include aspects of shelf life studies, where product is typically held at a given time-temp combination. These studies may use specific references such as using USP <51>, or reference could include specific microorganisms, and criteria to determine effectiveness (such as log reduction).

Another example is determination of if a product requires refrigeration. For this, we first start with the food product itself, which has a specific combination of pH and water activity to prevent growth of groups of pathogens. Once we have this information, we don’t have to look at broad range of organisms, but can look at specific organisms. The remaining potential threats become challenge organisms for the study. We store the product at room temperature and test for these challenge organisms.

For more information on Special Projects, contact Eurofins US or email Bill Centrella at WilliamCentrella@EurofinsUS.com

Purnendu C. Vasavada, Ph.D., Professor Emeritus at University of Wisconsin

What Should You Know About Food Safety Testing?

By Sangita Viswanathan
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Purnendu C. Vasavada, Ph.D., Professor Emeritus at University of Wisconsin

Food safety is in the news. Recent food industry, regulatory and consumer trends stress proactive, systematic and preventive approach to food safety by managing food hazards and risks. Testing for food safety hazards, particularly microbial hazards and allergens throughout the food production and processing chain is becoming increasingly important in assuring food safety. Food testing is also becoming important for detection of adulteration.

In next week’s Food Safety Consortium to be held in Schaumburg, IL, Purnendu C. Vasavada, Ph.D., Professor Emeritus at University of Wisconsin, River Falls, and President of PCV & Associates, LLC, will discuss trends in the food safety testing market and approaches for testing of food and food plant environment, emphasizing microbial and other significant food hazards. In this article, PC, as he is popularly referred to, gives a sneak-peek into his presentation.

Food Safety Tech (FST): You will be speaking about the Food Testing Market – what are some broad trends that you are seeing?

PC: Food Microbiology testing is increasing worldwide but majority of testing is still dealing with food quality assurance and ingredient and product testing. Testing for pathogens seem to be driven by regulatory requirement. According to recent market reports, 76 percent of test volume in North America is for routine microbiology. In the EU and Asia, routine microbiology accounts for 81 percent and 72 percent of test volume, respectively.

Most pathogen testing is for Salmonella, E. Coli 057:H7 and Stex, Listeria and as L. monocytogenes. There is an increasing interest in testing for Campylobacter.

Testing of in-process and environmental samples is more common in NA and Europe. In Asia in-process/environmental testing only accounts for 9 percent of total test volume.

FST: In your presentation at the Consortium, what will you talk about FSMA and its impact on food safety testing?

PC: I plan to include a brief discussion on testing as related to monitoring and verification of Preventive Controls.

FST: Where is food safety testing headed, and what should food safety managers keep in mind?

PC: Given the emphasis on supply chain management and process control to manage identified hazards in preventive mode, food safety managers should understand testing internal and external testing requirements and complexity of sampling, testing tools and approaches not simply focus on cost aspects. Even if testing is outsourced, becoming familiar with various methods and testing tools will be necessary.

FST: Who should attend your presentation and why?

PC: Plant managers, quality assurance supervisors, marketing managers, food safety testing methods, equipment and service providers as well as anyone interested in food safety testing would find this presentation very useful and relevant to their day-to-day activities.

Are you registered for the Food Safety Consortium yet? Sign up now, and hear from over 70 experts in this area.

Sangita Viswanathan, Former Editor-in-Chief, FoodSafetyTech

Interview: “Look at your Food Safety Testing Needs, and Carefully Assess your Lab”

By Sangita Viswanathan
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Sangita Viswanathan, Former Editor-in-Chief, FoodSafetyTech

Food Safety Tech (FST): What’s so important about IS0 17025 accreditation?

Shaw: The ISO 17025 standard is a gold standard for lab quality. The standard is system based, and not prescriptive, so there can be a lot of differences in how it’s implemented. ISO requires you to have a procedure to do something, it doesn’t tell you what that procedure is. For instance, the standard requires you to have a procedure for customer complaints, however the lab can either have a very basic system of recording and investigating these complaints, or it could process that complaint and get to the root cause, and correct the nonconformance, so that the problem wouldn’t be repeated. Similarly when it comes to personnel requirements, the standard can be interpreted as having competent people on staff, or having elaborate six-week long training programs and documenting this.

FST: How does laboratory design impact microbiology operations?

Shaw: Lab design is very important from both an operation and quality point of view. It’s important to keep in mind that you are dealing with potentially dangerous pathogens and contaminants, and after you have prepped and enriched the sample, and it’s positive for a pathogen, you have a huge number of microorganisms in that sample. You have to make sure that this is not moved back into the lab. Thus lab design has to ensure single directional flow of sample from one side of the lab to the other side, with both sample and personnel moving along the clean to dirty direction. Once samples come in, are prepped, enriched, incubated, and then tested, positive samples then are a threat to the lab, and the environment, in case there’s a spill or a bad technique in place.

From an efficiency point of view, LEAN is a big concept now. So lab design, if done well, can help realize efficiencies in consumables, personnel, minimizing foot traffic etc. If everything is set up correctly – in terms of reagents, equipment, testing kits etc – then you can reduce time and effort spent in gathering samples, and moving around the lab. At Eurofins, we take this very seriously. We have a team that’s dedicated to lab design process and engineering around our workflow, and believe investing resources in the necessary software system LIMS to drive up efficiencies.

FST: How should high risk samples be treated? Should customers notify the lab of hot samples?

Shaw: There are two schools of thought about this. The first one is we want to treat all samples the same, so that we don’t bias the technician. We barcode all samples in the same way, test them in the same way.

On the other hand, we don’t want to open the lab to unnecessary risk, and contaminate the lab. So we handle high-risk samples differently, by taking extra precautions. Sometimes, a customer can bring in a sample and say it has Salmonella, and needs to be tested. We will still run the sample through the same procedure, but will separate it from the other batches. We also have to take care to schedule testing of these positive samples carefully such as moving it towards the end of a shift or break.

FST: With changing rules for food safety testing, what’s changing with regards to documentation?

Shaw: It’s important, as always, to record anything that can affect the result of a test. Also clear time stamps must be documentation. When things happened, who did the preparation of the sample, who analyzed the sample? Consumption of media, test kits, chemicals and agents, or anything that was used in the analys, all must be clearly recorded. In some labs, all of the documentation is still in paper, and hence is a very manual process, while other labs are highly digitized and have the ability to track a lot of this information electronically.

FST: What are some practical challenges that food safety testing lab typically encounter?

Shaw: Labs typically face challenges with result validation, typos in documenting test results, and customer requests around retest situations. When it comes to reporting, it’s important to have a number of eyes looking at your data, to make sure that it makes complete sense. For instance, if you are testing a product for coliform bacteria, and specifically for E.coli, then the latter number cannot be higher than the total coliform number. If there is, it means there’s an issue with the analysis.

Typos with lab results, sample number etc. are other issues that every lab suffers on a day to day basis. Fundamentally, humans make errors, but as technology evolves, and systems learn to interface better with each other, such errors can be minimized.

Another challenge relates to situations when we have released the CoA and then the customer calls us to modify the lot numbers. This is a gray area, and potentially could become problematic. In such situations, when the customer requires something to changed, it’s prudent to have some kind of documentation about this, clearly specifying that it was a customer-initiated request. Of course, such situations also have an ethical component to it, so they need to be handled carefully.

Accommodating requests for retesting samples can also be a challenge. For instance, you test a sample on Day 1, and are also to test again on Day 3, you could get different results. Getting similar results with microorganisms, even when the samples are homogenized etc., is challenging and not realistic if you consider that the microorganism could increase or decrease in those few days.

Overall, Shaw encourages food companies to take a careful look at their food safety testing needs and the lab’s abilities. “Don’t just accept an ISO certificate. Ask to look at the labs, their processes etc. Good labs will encourage that, while the not so robust ones, may not accept that request, even though they have an ISO certificate, and that, in my mind, should raise a red flag,” explains Shaw.

Microbiological Method Validation: The Elephant in the Lab

By Evan Henke, PhD, MPH
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Although commonly overlooked, microbiological method validation studies are the linchpins of entire quality programs, and method validations done without rigor are crippling our industry’s ability to truly ensure the quality and safety of foods on a daily basis.

Food quality managers, it is time we discussed the critical importance of validation studies in the quality lab. Although commonly overlooked, microbiological method validation studies are the linchpins of entire quality programs, and method validations done without rigor are crippling our industry’s ability to truly ensure the quality and safety of foods on a daily basis. This article discusses the purpose and importance of microbiological method validation studies and why the food industry should insist on validation study designs of maximum rigor and validity.

What is a microbiological method, and what exactly is a validation study?

A microbiological method, for the purposes of this discussion, is any microbiology test or assay used in the food industry. It may be a test for indicator organisms such as Coliforms or yeast and mold, pathogens such as Salmonella or E. coli O157, or toxins secreted by microorganisms such as Staphylococcal enterotoxin.

A validation study is a one-time study that food safety risk managers complete in order to assure themselves that a new microbiological method produces accurate results that will enable them to effectively measure and manage food safety risk. A validation study is conducted in the actual lab where testing will be performed, with current laboratory analysts, with the specific formulations of foods that are tested regularly.

Food industry regulators and certifying bodies such as SQF expect food producers to use microbiological test methods that are proven fit for use on specific foods. If we are to draw inferences about the fitness of a new test method on specific foods, then we must study how that new test method compares to an accepted reference method, or “gold standard” method. Reference methods are those written in the Food and Drug Administration’s Bacteriological Analytical Manual, the United States Department of Agriculture’s Microbiological Laboratory Guidebook, or ISO methods. Regulators and experts agree that these methods represent the standard to which all other tests should measure up. Methods certified by the Association of Analytical Communities (AOAC) are not considered reference methods and must be validated as fit for use on foods that are appreciably different from the matrices studied. Likewise, AOAC Performance Tested Method (PTM) and Official Methods of Analysis (OMA) certificates are not substitutes for internal validation studies in any given food plant.

In my experience working with quality labs across the United States, I have seen several different validation study designs used to evaluate alternative, more rapid and cost-effective microbiological methods. Some common validation study designs are shown in Table 1. Multiple alternative tests are available, however an internal validation study is needed regardless of the test kit manufacturer. Rarely does a validation study include a comparison to agar plates, which are required for almost every microbiological reference method. Material costs, labor costs, and emergency situations typically prohibit food labs from conducting a rigorous validation study that can speak to the performance of a new method in relation to the current gold standard.

Table 1: Scientific Questions Inherent in Food Microbiology Method Validation Study Designs 

 Validation Study Design  Inherent Scientific Question  Does Study Explain Performance
of New Test?
Test positive or spiked samples side by side on reference method and the new test  Does the test perform comparably to the reference method on my food? Yes 
Test positive or spiked samples on the new test  Regardless of accuracy, can the test detect certain or specific bacteria in my food?   No, but may be useful to understand workflow
Test any samples side by side on current AOAC certified method and new test  How do the new test’s results compare to my current AOAC certified method on my food?  No, but may be useful to understand workflow 
Test any positive or negative samples on the new test  Will the new test’s workflow improve my lab’s efficiency?  No, but may be useful to understand workflow 
This table presents several validation study designs common in the food industry and the scientific questions that are addressed by each design.

It is in the best interests of food producers and the public’s health to conduct rigorous validation studies that give food safety risk managers good information to make correct risk management decisions. In theory, some percentage of unsolved epidemiological foodborne illness clusters must be due to incorrect risk management decisions that allowed contaminated products to reach the market. At the same time, some percentage of all food lot rejections and recalls must be made incorrectly. A portion of these events must be related to food matrix interference that yielded incorrect microbiological results and caused the wrong risk management decision. As they say, “Garbage in, garbage out.”

In addition, including a comparison to agar reference methods in your microbiological method validation study is critical, as it reduces your chances of making an incorrect risk management decision.

Look at things this way: Plants certified with a GFSI accredited quality scheme have already put in effort to ensure analytical equipment such as thermometers and scales are calibrated. Similarly, validating microbiological methods against a reference method is equally if not more important. Finished product microbiology results inform decisions made every day that affect your profits and losses, and those results are likely a primary metric you use to study the effectiveness of your prerequisite programs and preventative controls.

Consider a quality lab that is using an alternative microbiological method that has not been rigorously validated with the plant’s specific foods. Unknown to the lab, the test results every day are twice as variable as the reference agar method and are frequently inaccurate relative to the plant’s product specifications. A rigorous method validation would demonstrate that results on the current method vary widely, while the same samples are consistent with a reference method. This well-intentioned plant is unknowingly making incorrect risk management decisions not just multiple times per year, but multiple times per week, either accidentally releasing contaminated product, reworking product that is acceptable, or disposing of perfectly good product. For the millions of dollars the food producer invests in prerequisite programs, preventative controls, quality personnel, and testing, the plant is unable to optimize their food safety risk management simply due to an unknown and overlooked incompatibility of the microbiological method with the plant’s product.

In my estimation, the costs of rigorously validating a microbiological method on all of your food products outweigh the potential hidden costs that could result from method incompatibility. The business case justifying the costs of a validation study are strong and compelling. And learning how to apply current microbiological methods specific to your foods is not as hard as you might think, considering the large host of test manufacturers, third-party labs, consultants, food safety extensions, and industry groups available to regularly provide study design education and services.