Whether you are just setting up your environmental Listeria monitoring program or reassessing your existing program, there are basic elements that you will want to include. A general overview of these elements is provided below. In addition to these elements, an effective environmental Listeria monitoring program must have expressed commitment from the senior management or executives within the company. “For food safety to succeed in an organization, the most important element is management commitment,” notes a previous article in Food Safety Magazine.[1] This can be true for Hazard Analysis and Critical Control Points (HACCP) and prerequisite programs such as Good Manufacturing Practices (GMPs), allergen management and environmental monitoring. Consequently, it is important that as you develop your environmental monitoring program, you ensure that senior management and executives are educated as to why the program is necessary, how it will be implemented and what will be done with the data that are generated.

Rationale for Environmental Monitoring
It is commonly stated that before you do any type of testing, you should ask, “Why are we conducting the testing and what will we do with the results?” This is a good maxim to apply with regard to environmental testing because gathering data that point to a potential problem but not having a plan to address it can result in regulatory control actions. For example, if you are collecting environmental Listeria swabs in a raw environment during operations and receive positive results, you will be expected to take actions to eliminate the positive results, which, in a raw environment, may be quite challenging.

So, when you ask yourself why you are conducting environmental monitoring, the likelihood is that you are doing so for the following reasons:

•    You are seeking to identify the sources of entry, harborage and translocation of Listeria in the plant.

•    The locations where you will swab are those areas where finished product could be exposed and susceptible to contamination.

•    When you find those sources, you will conduct an investigation as to how the organism established itself in the locations where it was found.

•    Once it’s found, you will destroy the organism and eliminate the sources of entry, movement and harborage.

In addition, you will include as part of your rationale that you are conforming to the requirements of the appropriate regulatory agency or agencies. Plants operating under U.S. Department of Agriculture (USDA) jurisdiction and making ready-to-eat (RTE) meat and poultry products already are required to have programs conforming to the requirements of 9 C.F.R. 430.4 — “Control of Listeria monocytogenes in post-lethality exposed ready-to-eat products.” These regulations were issued in 2003 and outline the agency requirements for verification that RTE meat and poultry products are not adulterated by Listeria monocytogenes (Lm). In addition, this year, the U.S. Food and Drug Administration has proposed rules for environmental Listeria monitoring in plants that produce RTE products that fall under its jurisdiction.

The person writing the environmental program should have good working knowledge of regulatory requirements that must be met as well as experience preparing an effective monitoring program. To help with the writing of an effective monitoring program, the “who, what, when, where, why and how” are addressed below. Many of the recommendations are based on my experience.

Locations to Swab
Once you have established the rationale and objectives for your program, you will then determine the area of the plant where swabs will be collected as well as the specific sites for swabbing. In general, the locations for swabbing will be those areas where a finished product is exposed to the environment prior to final packaging and can then be contaminated or recontaminated. More often, this is a fully prepared product that is RTE and does not require cooking to lethality by the end consumer.

Once you have identified the areas in the plant, postlethality and prepackaging, you will want to identify specific sites that will include equipment and the environment that will be swabbed. Most people are familiar with the “zone concept” for environmental swabbing, which establishes areas from those that contact the food to those that are furthest away but can contribute to entry of Listeria into the environment. Zones are broken down as follows:

•    Zone 1: Direct Contact. These are surfaces that come in direct contact with RTE ingredients or finished product. This can include inner surfaces of ingredient mixers or fillers, stainless steel tables, contact utensils, conveyor belts and packaging.

•    Zone 2: Indirect Contact. This includes surfaces that are not in direct contact with RTE ingredients or finished product but are in very close proximity. If these surfaces are contaminated, they can contaminate product through incidental contact, condensation or harborage niches. Included in this zone are equipment framing, control panels, pass-through windows and other locations near the product.

•   Zone 3: Noncontact. These areas include environmental locations such as floors, walls, drains, pallets, transport equipment and overheads. They are usually not sources of direct contamination to product but can be harborage locations for Listeria that can be translocated or moved from one place to another by equipment, personnel or personnel practices.

•   Zone 4: Auxiliary Areas. These include zones outside the production area that do not receive regular cleaning and sanitizing, where Listeria can harbor and then be translocated to the production environment. This may include the maintenance shop, ingredient storage areas and warehouses.

The decision to swab in zone 4 may depend on the processes you have in place to control personnel or equipment movement between these areas. If you have good controls or you utilize captive footwear and boot scrubbers, you may decide that swabbing these areas is not crucial to your program. Bruce Tompkin once wrote, “It is realistic to expect that L. monocytogenes will continue to be introduced into the environment in which RTE foods are exposed for further processing or packaging.”[2] With that in mind, you will want to determine whether the reexposure is from a zone 4 area, which will help you decide if and when it will be swabbed.

There may be several criteria that you use to decide where to swab: generic swab results, visual appearance or prior experiences. Regardless of the reason, your objective is to aggressively seek and find Listeria: Find where it enters the plant, where it harbors and where it moves. Then once you find it, you have a better opportunity to destroy it.

Frequency of Swabbing
The frequency of environmental swabbing, along with the number of swabs collected, will vary depending on the products you make, the potential for exposure and the potential for growth after the product is packaged. USDA regulations for swabbing are based on the “alternative” into which products fall. Alternatives are defined as follows:

•    Alternative 1: The product includes a postlethality treatment that has been validated for effectiveness and an antimicrobial agent or process to eliminate or suppress the growth of the target organism.

•    Alternative 2: The product receives a postlethality treatment that may include an antimicrobial agent or a process (e.g., freezing) that suppresses growth of the target organism.

•    Alternative 3: The product is not treated with an antimicrobial agent or process and relies on plant sanitation to control the target organism.

Based on these criteria, the frequency of your swabbing may vary. However, depending on the alternative into which your products fall, you will need to justify your frequency, number of swabs and site selection. You will have to be able to demonstrate that your program is sufficient to effectively control Lm or Listeria spp. if you are using Listeria spp. as an indicator organism.

Can You Believe It?
Upon finding out that the rate of positive results had decreased, I witnessed one plant manager who responded, “Good. Now that the rate of positive results has decreased, we can stop this testing, it’s costing us money!”

You will also want to consider the types of products, consumers of the products, the possible mishandling of your products, the data generated from your monitoring program and the risk assessment documented in your HACCP plan. These can also be used to help determine your frequency of swabbing. Also keep in mind, USDA Food Safety and Inspection Service will collect RTE product samples for pathogen testing, and the frequency of their testing may depend on the alternative. Products in alternative 3 will probably have a higher frequency of testing than those in alternative 1 or 2.

The Swabbing and Analysis Process
The swab locations, once they are identified, will be swabbed on a set frequency with each location identified having an equal opportunity to be selected. This is best accomplished by using something as simple as a random-number generator from Excel or may be done with lab information management software that will maintain the list of locations, the swab result for each location and the percentage of those locations that are positive.

Sterile sample collection technique to prevent unintentional contamination of the swabs, to ensure that the appropriate pressure is applied and that the appropriate surface area is swabbed is critical. A rule of thumb is to apply firm pressure, approximately 3 pounds, to the swab, so that if there are imperfections in the surface being sampled, there is an opportunity to collect what may be in the crevices.

Great Moments in Environmental Swabbing
While I was working with a plant that was having significant challenges with findings of Listeria in the environment, a meeting was held with the management team to discuss the findings. It was apparent that the maintenance manager was getting extremely frustrated with the continual findings. During the meeting, he finally blurted out, “The reason that we are getting all of these positives is because the FSQA [food safety/quality assurance] personnel are going crazy swabbing; they’re pressing too hard!” I calmly tried to explain that they were trying to find the sources of the positives so that we could eliminate them, but he persisted that the swabbing efforts were crazy. Once again, I tried to be calm and asked him what he meant by “crazy.” He pointed his finger in my face and yelled, “You are!”

That’s not the first time I’ve been accused of being crazy, but it does bring me back to the objective of the program, which is to find locations where Listeria lives in the plant so that you can destroy it. Consequently, don’t blame the FSQA personnel for finding it; work together to determine how you are going to eliminate it!

The Nuts and Bolts of Swabbing
Generally, it’s preferred that prehydrated sponges are used, as they are packed in a neutralizing broth that will offset any residual sanitizer that may be present on the surface. In addition, they are better able to swab a broad area compared with Q-tips®. However, Q-tips can be used to access areas that sponges cannot reach. The area being swabbed must also be a consideration. Since the analysis for environmental Listeria will probably be qualitative, the area swabbed may not be a standard 4-inch-by-4-inch grid. If you are swabbing the horn of a hot dog peeler, then you want to swab as much of the horn as possible. If you are swabbing a floor area, then swab as much of the surface as you can reach (Figure 1). For areas that are difficult to reach, a swab pole that holds the sponge on a stick is a great tool for accessing overheads (Figure 2). Again, you are trying to find it if it’s there!

Once swabs are collected, then they will be analyzed for Listeria, but this now leads you to three additional decisions for your program:

•    Who will do the analysis, an internal lab or a third-party lab?

•    What analytical method will be used?

•    Will you analyze for Lm or use Listeria spp. as an indicator organism?

The decisions for these questions will probably be based on company policies, cost and willingness to accept risk.

When considering internal testing, you must determine whether the testing method might expose the plant to an unintended contamination from actually “growing” the organism in the lab. Some methods require that the swab be enriched, which actually grows the organism to levels that can be detected. If the lab is physically separate from the plant, the microbiology technician is well educated and there are Good Laboratory Practices in place to prevent the spread of the organism, then internal lab testing may be an option. The reasons for selecting a third-party lab will be that the plant may not have good spatial separation of the lab, or the company sees that results from an accredited outside lab eliminate the potential for conflict of interest.

The method selected may be one of timing. Cultural methods take longer than the rapid methods that are available but are usually less expensive. If fast results are critical, because of limited shelf life of the product, then a rapid method may be worth a higher testing cost.

Most of the time, it is recommended that the test be for Listeria spp., since this provides you with an idea of whether the environment is hospitable to supporting Lm. In other words, Listeria spp. is the indicator organism for Lm and provides you with valuable information about where greater control is required for the environment. However, if the plant decides to test for Lm, it is highly recommended that if swabs are collected from direct product contact surfaces, that product is placed on hold and not leave the direct control of the company until negative results are received. Regulatory agencies will consider product to be adulterated if it is manufactured on, or comes in contact with, equipment that is positive for Lm.

Positive Results, Investigations and Elimination
If all results received from the environmental swabbing are negative, then the sites swabbed can return to their normal, routine and random selection process. However, if a site or sites are positive, then the plant must initiate a process to determine why the site is positive for Listeria and then prevent a positive result from reoccurring. One approach to positive results is a three-step process that includes investigation, corrective action and verification.

Investigations should be conducted within 24 hours of the receipt of a positive result. This means that if the result is received on a Tuesday, the investigation will be conducted no later than Wednesday. The investigative team will be cross-functional, including personnel from FSQA, production, sanitation and maintenance. The team will have a scribe to document findings, a swabber to collect swabs from potential contributing sources and investigators who have familiarity with the process and the equipment. We like to train our teams to use the Ishikawa approach to investigations, which includes evaluating “Man” (personnel practices, conformance to GMPs), “Machine” (insanitary design), “Material” (ingredients added postlethality), “Method” (cleaning procedures, operational sanitation methods) and “Environment” (the physical facility). The team will have the authority to take swabs when warranted, take pictures of findings and open equipment or panels if it is determined that they need access as part of their investigation. Once the observations have been documented, the team will meet with plant management to review the findings and to identify corrective actions, responsibilities and timing.

The corrective actions are designed to destroy Listeria when it is found. This may include deep cleaning through breakdown of equipment, use of chemicals that target Listeria (e.g., quaternary ammonium compounds, peracetic acid) or use of chemicals at high levels to achieve greater destruction of the organism. The actions may also include, depending on the findings, prevention of translocation of the organism (e.g., controlling personnel or equipment movement from raw to RTE, reducing water usage in production), repair of equipment or the environment that may harbor Listeria (e.g., cracks in floors, insanitary welds, elimination of hollow rollers) or improvement of sanitation processes.

A Day in the Life
While working with a plant sanitation crew to reduce the amount of water used for operation cleaning, I was informed by a corporate vice president that “it’s OK for them to use a lot of water…Listeria floats in water.”

Once the corrective actions have been implemented, the plant will verify that they have been effective by swabbing the original positive site multiple times to ensure that Listeria has been eliminated. This usually means that the site will be swabbed on multiple days, preoperation and twice during operation, to verify the effectiveness of the actions. If there are no more positives on the original site, then it can be determined the actions were effective and the plant can return to normal, routine swabbing. However the program must also identify when the plant will implement “hold-and-test” procedures following a Listeria spp.-positive result on a direct contact surface.

A well-thought-out and designed environmental swabbing program can allow a company to determine the sanitary design and operation of its facility or where improvements can be made to protect its products from adulteration with environmental pathogens. To be effective, the program must be written to ensure that there are aggressive efforts to seek out Listeria and then, once it is found, destroy the organism. This must happen with the support and commitment of the company’s senior management or executive leadership to be most effective.   

Michael Cramer, CQA, is the senior director, food safety and quality assurance, for Ajinomoto Windsor and a member of the Editorial Advisory Board of Food Safety Magazine.

1. Ades, G et al. 2014. “Food Safety Culture: Insurance Against Catastrophe.” Food Safety Magazine 20:44–49, 64.
2. Tompkin, RB. 2002. “Control of Listeria monocytogenes in the Food-Processing Environment.” J Food Prot 65(4):709–725.