Tag Archives: ATP

Wendy White

Understanding the True Purpose of Environmental Monitoring Programs

By Wendy Wade White
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Wendy White

 Salmonella and Listeria are among the most prevalent foodborne pathogens, causing untold illnesses and a significant number of recalls each year. Experts have determined that the source of this contamination often comes from the manufacturing facility. Five years ago, the FDA published, Draft Guidance for Industry: Control of Listeria Monocytogenes in Ready-To-Eat Foods (we’ve also been promised a similar guidance document for Salmonella). The Food Safety Modernization Act’s Preventive Controls for Human Foods also contains provisions for evaluation of environmental pathogens in a ready-to-eat hazard analysis.

Employee in cheese plant
A product’s risk level varies based on the amount of pre-packaging exposure to the environment and direct handling by employees.

The challenge with these pathogens is that they are often found in the surrounding environment, and once they enter a facility and become entrenched, these residential pathogens can cause sporadic contamination that is very hard to pinpoint. The best way to prevent this type of contamination is to design and implement a robust Environmental Monitoring Program (EMP), and many manufacturers have added these surveillance programs to their food safety systems.

Unfortunately, many do not understand that the true purpose of EMPs is to seek and destroy residential microorganisms of concern that are living inside facilities before they have a chance to proliferate and contaminate products. This key control involves swabbing surfaces around the facility in the hopes of finding any of these residential pathogens or spoilage organisms. Having a robust, written EMP that includes clear action levels for unsatisfactory results and corresponding corrective actions will help manage pathogen positives and mitigate disaster.

Defining the EMP Scope and Balancing Resources

When designing an EMP, it’s easy to understand how expensive they can become. The question is, “How extensive does your EMP really need to be?” It’s best to start with a risk assessment to understand the program size and then estimate a realistic budget.

These programs are more necessary for ready-to-eat facilities, especially ones in which the post-processed product is exposed to the environment before being safely packaged. Risk is determined by how much pre-packaging exposure the product receives, the amount of direct handling by employees, and the condition of the equipment and surrounding facility. Use this risk analysis to determine how much sampling must be done to properly survey the facility. The scope of the program (and therefore the budget) must be balanced with the risk (severity and likelihood) of contamination.

It is then important to understand the microorganism(s) of concern for your products, facility, and processes. For example, should you stick to true pathogen testing or indicator organisms, such as Aerobic Plate Count (APC or TPC), Enterobacter, or Total Coliform tests? If you do test for pathogens, Listeria is more appropriate for wet processing environments and Salmonella better for dry processing; you might need to test for both. Sometimes its beneficial to evaluate spoilage organisms, such as yeast and mold testing, depending on the risk. For example, a ketchup facility may be less worried about residential pathogens than osmophilic yeast.

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Next, one must determine the frequency and number of swabs that should be taken. Most facilities are large and contain thousands of potential hiding spots for microorganisms. For this reason, understanding your facility’s risk and available resources, and prioritizing the swabbing site selection can help maximize efforts. Will a dozen swabs every quarter be sufficient? What is your level of confidence that the sampling program is sufficient to find any hidden biological hazards? Being logical about the target microorganisms and swab frequency/number can help control the budget and allow for better use of resources to accomplish the true EMP goal, minimizing risk to your product.

Creating an Acceptable Site List

Just as important as defining the microbe of concern and the frequency/number of swabs is creating a good site list. An EMP expert once advised to, “think like Salmonella.” Where is our target pathogen/microbe of concern most likely to be hiding? Factors to consider are potential ingress points (roof leaks, employee shoes), opportunities for travel (water/air flow points like drains, foot or wheeled traffic routes), and likely niches (cracks and crevasses). Also important are areas that are often missed by the sanitation crew due to inaccessibility.

Organizing surfaces into zones is a good means of prioritizing swabbing. Zone 1 (food-contact surfaces) and Zone 2 (surfaces adjacent to food-contact surfaces) are cleaned often and not as likely to harbor hidden caches of microbes. It’s important to conduct routine verification testing of these equipment surfaces to evaluate the performance of sanitation, but this is somewhat different than the true purpose of EMP, which is to seek and destroy residential biological hazards. Zone 3 surfaces (those inside production areas but not immediately near food-contact surfaces) are the best focus for an EMP site list, and most of the surface swabbing should be concentrated in these areas.

Consider areas within the facility that could harbor microorganisms and allow biofilms to develop. Cracks, areas regularly exposed to water, and places that are very hard to reach/clean are all likely candidates. These include underneath equipment frames, inside motor casings and pumps, deep inside drains, underneath ramps and stairs and inside air vents/AC units. Cast a wide net, ensuring that all areas are rotated through the swabbing list, while prioritizing the high-risk locations.

The main stumbling block that managers face when designing EMP is challenging themselves to find problems, because once you find an issue, you must deal with the consequences.

Having a Game Plan for Unsatisfactory Results

The best way to mitigate the fear of success (finding a residential pathogen or microbial issue) is to be prepared with an action plan. This starts by defining what constitutes an unacceptable result. Pathogen results are easy (the presence of a pathogen is always unsatisfactory) but the quantitative results from indicator organisms can be tricky. How high do your Enterobacter or yeast/mold results need to be before they trigger action? What is that action?

Family in grocery store
Environmental monitoring programs are most needed in facilities that process and package ready to eat foods.

It’s all too common for unsatisfactory swabs to reemerge a few weeks after initial corrective actions because the true source of the contamination wasn’t found. Requirements for EMP corrective actions are often limited to 1) Reclean 2) Reswab and 3) Retrain. This is extremely limited and doesn’t really address the root cause. Vector swabbing is a great tool to identify root cause, as well as conduct an evaluation of variables that could spread contamination. For example, Listeria found in a drain might have originated by an unsealed wall/floor junction, a perfect microbial niche. When the crack is flooded, the biofilm periodically releases fresh contamination to spread across the floor and into the original identified drain.

Different results should trigger different responses. Certainly, reclean/retest/retrain is a smart approach, but finding the true source of the contamination and taking steps to eliminate it is vital. This might involve special cleaning, such as fogging or hiring a consultant. It might require a redesign of equipment or replace and repair of damaged or vulnerable areas. Ensure that all unsatisfactory results involve an investigation, graph results to identify trends, and communication of findings to all appropriate stakeholders.

EMP Review and Reevaluation

EMP doesn’t have to be a static program, and there’s no “one-size fits all” approach. It’s recommended to design your program based on risk and the above-mentioned variables, implement, and monitor the results. If you never find unsatisfactory results, you might need to increase your frequency/number of swabs or reevaluate your site list. Are you properly challenging yourself? Are you REALLY trying to find problems or just going through the motions to satisfy some requirement? You know your products, facility, and employees and should be able to make these determinations. Don’t be afraid to revise your EMP as a result of historical data and changing variables inside the facility. This might involve increasing your frequency/number of swabs, but the reverse might also be appropriate. Sometimes EMP can be scaled back, and those resources better used elsewhere.

The best approach to a well-written EMP is to understand the scope by considering the risk and applicable variables, employing thoughtful and risk-based logic to the design, and planning for potential unsatisfactory results with thorough corrective actions. Be mindful the true purpose of Environmental Monitoring Programs, which is to seek and destroy harmful microorganisms of concern inside your facility. A robust EMP, coupled with proper training, implementation, monitoring/trending, and communication, will go a long way towards peace of mind that your facility isn’t harboring a potential, biological hazard threat.


Using ATP-based Methods for Cleaning and Sanitation Verification

By Camila Gadotti, M.S., Michael Hughes
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There are several factors that must be considered when selecting a reliable and accurate system for detecting adenosine triphosphate.

A common way to assess the effectiveness of cleaning and sanitation programs in food manufacturing facilities is through the use of methods that detect adenosine triphosphate (ATP). Methods based on ATP detection are inexpensive and rapid, and provide the ability to perform onsite in real-time. There are several manufacturers of ATP-based methods, but choosing the most reliable one can be a daunting task. This article will discuss how these methods work and which factors should be considered to make an informed purchasing decision.

ATP is the universal energy currency in all living cells. It is present in all viable microorganisms (with the exception of viruses) and in foodstuffs. High amounts of ATP can be found in some fresh foods like vegetables, while other foods, especially highly processed foods such as fats, oils or sugar, contain very low amounts of this molecule. It is also important to know that ATP can be found in the environment in its free form hours after a cell has died.1 An ATP bioluminescence assay operates on the principle that ATP in food/food residues and microorganisms, in the presence of a luciferin/luciferase complex, leads to light emission. This light can be measured quantitatively by a luminometer (light-detecting instrument), with results available in 10–40 seconds. The amount of light emitted is proportional to the amount of ATP on a surface and hence its cleanliness. The light emitted is typically measured in relative light units (RLUs), calibrated for each make of instrument and set of reagents. Therefore, the readings obtained from assessing the cleaning of food manufacturing facilities need to be compared with baseline data representing acceptable clean values.

Varying Optical Components

Luminometers have evolved over the years from very large and cumbersome in size to small handheld models that can be used anywhere within a manufacturing facility. Although several components are housed inside these instruments, the optical component is the most important part of a luminometer. Used to detect light coming from the ATP/luciferin/luciferase reaction, the optical component is the defining factor related to luminometer reliability, sensitivity and repeatability. Good luminometers use a photomultiplier tube (PMT) in the light detection system; however, as part of the drive toward cheaper and smaller instruments, some manufacturers have replaced PMTs with less-sensitive photodiode-based systems. When using photodiodes, the swab chemistry must be adapted to produce more intense light. This results in a shorter duration of light, decreasing the time window allotted to place the swab in the luminometer and obtain an accurate read. A PMT, however, multiplies the electrical current produced when light strikes it by millions of times, allowing this optical device to detect a single photon. This approach emits light over a longer period of time. Although the weight of the system is also dependent on factors such as the battery, case and the display screen, a luminometer constructed with a photodiode will generally weigh less than a luminometer constructed with a PMT, since the former is smaller than the latter.

Sensitivity Testing

When an ATP hygiene monitoring system has poor sensitivity or repeatability, there is substantial risk that the test result does not truly represent the hygienic status of the location tested. Therefore, it may provide false positives leading to unnecessary chemical and labor costs and production delays, or false negatives leading to the use of contaminated pieces of equipment. A system that is sensitive to low-level contamination of a surface by microorganisms and/or food residues allows sanitarians to more accurately understand the status of a test point. The ability of a system to repeat results gives one peace of mind that the result is reliable and the actions taken are appropriate. To test different ATP systems for sensitivity, one can run the following simple test using at least eight swabs per system:

•    Make at least four serial dilutions of a microbial culture and a food product in a sterile phosphate buffer solution.
•    Using an accurate pipette, dispense 20 μl of these dilutions carefully onto the tip of the swabs of each ATP system and read the swabs in the respective luminometer, following the manufacturer’s instructions.
•    Use caution when dispensing the inoculum onto the swab head to prevent any sample loss or spillage. In addition, it is very important the swabs are inoculated immediately prior to reading, which means that each swab should be inoculated one at a time and read in the respective luminometer. Repeat this process for all the swabs.


To test different ATP systems for sensitivity, one can run a simple test using at least eight swabs per system. Photo courtesy of 3M

The most sensitive system will be the one that results in the most “fail results” (using the manufacturers’ recommended pass/caution/fail limits).

One can also test different ATP systems for repeatability by the following test:

•    Prepare a dilution of a standard ATP positive control or a food product such as fluid milk in a sterile phosphate buffer. If using a standard ATP positive control, follow the manufacturer’s direction to prepare dilution. If using fluid milk, add 1 ml of milk into 99 ml of phosphate buffer.
•    Using an accurate pipette, dispense 20 μl of this standard onto the tip of the swabs of each ATP system and read these swabs in their respective luminometer, following the manufacturer’s instructions.
•    Prepare and read at least 10 swabs for each system you are evaluating, and capture the results on a digital spreadsheet.
•    Once all 10 swab results (for each system) are in the spreadsheet, calculate the mean (=average) and standard deviation (=stdev) for each system’s data set. Divide the standard deviation by the mean and transform the result in percentage; this value is called the coefficient of variation percentage (CV%).
The test with the lowest CV% is the most repeatable and will provide the most reliable information to help make the correct decisions for a food manufacturing facility.

Choosing the Right ATP System

There are many ATP systems available on the market to support cleaning and sanitation verification in manufacturing plants. Some systems are more reliable than others and will provide results that are meaningful, accurate and repeatable. Be sure, therefore, not to choose a system solely based on its price. Check for the quality of the instrument, ask the sales representative what kind of optical device is used in the construction of the instrument and, moreover, perform an evaluation running tests for both sensitivity and repeatability. It is also important to consider the functionality and usability of the software provided with the system to ensure that the software can be used to customize sample plans, store test results and produce reports and graphs.


  1. Jay, J. M., ‎Loessner, M. J., & Golden, D. A. (2008). Modern Food Microbiology.


About the Author:

Camila Gadotti, M.S., is a field technical service professional and Michael Hughes is a technical service professional with 3M Food Safety.