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ATP Assays Point Way to Greater Safety
Advances in ATP testing technology have improved assay performance
by Catherine Shaffer
Food contamination can be a devastating public relations disaster for a food or beverage manufacturer or restaurant. For example, the Michigan-based Bill Knapp’s restaurant chain never fully recovered from a food contamination scandal in the 1990s. Although the cause of the contamination was identified and eliminated, the chain struggled until it finally closed its doors in 2002. An even bigger scandal in 2008, involving Salmonella contamination of peanut products, led to the discovery of major sanitation issues at Peanut Corporation of America processing plants in Blakely, Ga., and Plainview, Texas. The contamination, which sickened hundreds of people and resulted in eight deaths, highlighted the importance of early detection of potential food safety hazards.
Congress is now preparing legislation (H.R. 875) establishing a new food safety administration (FSA) within the Department of Health and Human Services that will, among other things, demand more preventive measures against food contamination, in line with the best current scientific standards.
One of these tools is the adenosine triphosphate (ATP) assay, which tests for food, bacterial, and biofilm contamination on surfaces or in liquids. Once mainly a headache for third-shift cleaning crews, these tests are gaining greater importance as a tool for food quality control and safety. The ATP assay, usually performed as a surface swab, has emerged as an industry standard for detecting food residue or bacterial contamination on equipment and is one of the few tests that can predict a food safety crisis before it actually hits the news. For this reason, there’s a good chance that ATP assays will figure prominently in regulation and inspections under the new FSA.
Manufacturers of ATP tests have responded to increased interest by improving the tests’ sensitivity, accuracy, and ease of use and by bundling them with hardware and software that can more easily accommodate the workflow in a food processing facility.
A Closer Look
All living organisms use ATP for fuel. Because this universal “battery” is found in every living organism, from human beings to fungi, its presence is a good indication of the presence of biological materials. ATP assay technology couples an enzymatic ATP reaction to an indicator reaction. Most ATP assay systems use bioluminescence from firefly luciferase as a signal, which can then be detected by a portable luminometer. The test is nonspecific: It cannot identify the nature of contamination, only its presence.
ATP swabs can be used on many types of surfaces and equipment in a plant, such as conveyer belts, tanks, filler heads, saw blades, and grinders. Liquids can be tested using pipettes or “honey dipper” style devices for tanks and pipes and other types of equipment for which a four-inch by four-inch surface swab would not tell the whole story. A positive test indicates that cleaning was unsuccessful. This may be the result of the cleaning process, or it could be an early warning sign that equipment is wearing out, for example, and can no longer be effectively cleaned.
In the past, ATP assays have been used as a “quick and dirty” post-cleanup procedure, and sensitivity has not been much of a concern. Many plants are using them in a more quantitative fashion now, for collecting and saving data, for tracking trends over time, or as part of a hazard analysis and critical control points (HACCP) process. Because ATP testing is one of the few predictive diagnostic tools available in food industries, it plays an important role in many HACCP programs.
According to Paul Meighan, director for research and development at Hygiena International Ltd. (Waterford, England), HACCP customers comprise the largest portion of their business. Many of these customers require ATP assays that are as sensitive as possible. Hygiena pushes the boundaries of ATP assay sensitivity and accuracy with its forthcoming ultrasensitive Supersnap product, which will detect as few as a thousand bacteria. In order to increase the assay sensitivity, Hygiena used faster enzymes and optimized assay conditions.
“You either make the instrument more sensitive or the chemistry more sensitive,” Meighan said. Although more sensitive luminometers are available, focusing on the chemistry helps to keep the costs down for the end user. “The enzymology has reached maximum physical and kinetic output. The next stages are to now look to more sensitive luminometers as we at Hygiena are doing....The time will come where the ATP bioluminescence test may be as sensitive as it can be, at the attomole detection level now with only 6 logs to reach Avogadro’s number [single molecule detection].”
Meighan added that the main problem with sensitivity is not output of relative light units (RLUs) but the background noise. “If everything contains ATP, then all chemicals that go into ATP reagents will have intrinsic ATP which creates a signal above which is your measured signal. This is the battle that Hygiena has waged and now has won with backgrounds not measurable.”
Hardware and Software
Charm Sciences (Lawrence, Mass.) manufactures the swab kit and hardware components of their ATP assays and luminometer instrument and also develops the software and firmware. The vertical integration structure allows them to control every aspect of the product. One of the main innovations at Charm has been a wireless option on the luminometer that transmits ATP data in real time during the pre-op sanitation. This eliminates the sometimes lengthy delays involved in hygiene testing in a large plant.
Even with the sophisticated software and hardware environment, sensitivity is important. “It’s important to use a test that gives you confidence in your sanitation program,” said Gerard Ruth, Charm’s vice president. “If you’re using a test that’s insensitive, you have a false sense of security. It’s important to use instruments and tests that will allow for continuous improvement and not be satisfied with a test that fails to detect critical levels of ATP.”
Accuracy is a critical concern with an ATP device. All ATP tests are capable of detecting pure ATP. In nature, however, ATP occurs within a biological matrix, often inside bacterial membranes or behind the cell walls of plants and animals. In order to ensure reliability inside the manufacturing facility, some attention must be paid to the type of testing being done, the kinds of residues likely to be found, and the ability of a particular device to be accurate in detecting ATP within that context.
“Some ATP systems work beautifully with pure ATP and much less reliably in real world situations,” says Ken Davenport, PhD, Global Technical Services Product Specialist for 3M. “The industry is becoming more aware of those situations and becoming more discriminating in ... manufacturers for swabs.”
3M also includes a robust software package with its rapid hygiene ATP testing product, Clean-Trace. This software allows the user to create sample testing plans and group testing points together. The sample plans are transferred to the portable luminometer, where data is collected and transferred back onto the system. The system can then track the data and generate reports, graphs, and other types of analysis to help with decision-making in the plant. “It’s more than just an instant pass/fail,” Dr. Davenport said. “It’s being used to really track what’s happening in the plants. You get more value out of your ATP testing dollars using software to understand what’s happening in the cleaning process.”
ATP testing is not a solution for every problem in food quality and food safety, but it can be used to predict and prevent certain kinds of problems. Food residue that remains on a surface after cleaning can become a food source for microorganisms. In addition, off flavors or cross contaminations by allergens can result from failed cleaning processes. In the case of the peanut contamination scandal, a single source of contamination affected dozens of products distributed all over the world. Peanut products are not usually subject to pathogen testing because they have low water content. However, a regular program involving ATP swabbing of equipment and surfaces would surely have revealed the presence of animal feces in the plant. Thus, a predictive approach to hazards using tools that cast a wide net, like ATP testing, could theoretically avert unexpected hazards.
It is increasingly clear that a visual inspection cleaning process with end product testing is not enough to protect a food manufacturer from the repercussions of a major contamination incident. “If you’re not controlling your environment, you’re opening up your plant to significant risk,” Dr. Davenport said. “ATP is not the cure-all, but [it] can limit problems that come from poor cleaning.” Preventive methods such as HACCP add an extra dimension of control, and ATP testing is a solid tool for implementing such a program. Advances in ATP testing technology have improved the performance of the assays, while innovations in instrumentation and software have made it more than just a tool for spot-checking the cleanliness of a surface.
Shaffer is a freelance writer based in Ann Arbor, Mich. Reach her at firstname.lastname@example.org.