Seek & Destroy: Identifying and Controlling Listeria monocytogenes Growth Niches
By John Butts, Ph.D.
The latest U.S. Centers for Disease Control and Prevention (CDC) statistics show the rate of listeriosis continues to decline. We are now approaching our 2005 goal of a 50% reduction to less than 2.5 cases per million people, reducing the incidence of Listeria monocytogenes associated foodborne illness. This is occurring because industry is removing this pathogen from the cooked, ready-to-eat (RTE) product environment. Although Listeria's ubiquitous nature makes it impossible for the food industry to wholly eliminate this organism from the plant environment, it is an organism that we are better able to manage and control in plants producing foods identified as high risk.
This article is focused on a method that our company, Land O'Frost, has been using and improving on since the early 1990s to manage processing plant environments in a manner aimed at eliminating the root cause of product contamination by Listeria monocytogenes. No silver bullets will be revealed: This is simply a systematic method to apply known tools and techniques in a manner directed towards the greatest problem, the identification and control of growth niches. Known as "Seek & Destroy" (S&D) within Land O'Frost, this process is a tool that can be used to both identify and manage growth niches in equipment or facilities in three application areas, including (1) the effective investigation of a positive result, (2) the qualification of equipment or processes, and (3) the validation of the process. The effective application of this process enables other interventions to be applied at a level that will minimize their affect on consumer perception of product quality.
Defining Growth Niches
Many positive sites found during environmental monitoring are not growth niches; rather, they are transfer points (i.e., a product handler's gloved hands). In a food manufacturing operation that is cleaned daily, a growth niche can be defined as any location in which an organism is found after the flood sanitizing step. Since the organism is present in this location before the product comes to the line, it can be stated that transfer points are not growth niches, because the organism is eliminated during the cleaning and sanitizing process. As such, most pathogen monitoring and control sampling occur at transfer points, not the true harborage places or growth niches.
After analyzing Listeria outbreaks that occurred all over the world, former ConAgra microbiologist Bruce Tompkin introduced us to the following three scenarios of the sources of such contamination:
• Scenario One is a single, isolated event, where one package of product is contaminated via one transfer point in the process.
• Scenario Two is product contamination that occurs in only one specific batch or lot. Here, a line is contaminated via a transfer point, but where the normal cleaning will eliminate the contamination from the following production days.
• Scenario Three, and the one with which the food industry experiences its greatest problem, is a cluster. This is an outbreak involving multiple lots of food from a single source because there is a growth niche on a packaging line, for example, or there is a one-time construction event that affects several days of production.
These scenarios can be broken down into two modes of product contamination. The first is product contamination via transfer point, which is a Good Manufacturing Practices (GMP)-controlled event. The second is product contamination via growth niche. Clearly, the greatest priority for the food industry is to focus on the elimination and management of growth niches. We want to eliminate or control these growth niches, because DNA analysis has shown the same strain of Listeria monocytogenes to exist in a plant for several years.
Managing and Controlling Growth Niches
The food manufacturer must either remove by design or manage microbial growth niches as part of the production and sanitation process. Factors that give rise to the development of growth niches include equipment design problems, certain operational conditions such as product debris working its way into a uncleanable location, mid-shift cleanup, use of high pressure during cleaning, and existing product characteristics that cause excessive rinsing such as those encountered when producing sticky products.
In terms of design, equipment should be redesigned to eliminate or seal hollow areas, which are the single greatest example of areas that harbor growth niches. Therefore, any hollow areas of equipment (e.g., frames, rollers) must be eliminated where possible, or permanently sealed (caulking is not acceptable). Bolts, studs, mounting plates, brackets, junction boxes, name plates, end caps, sleeves and other such items must be continuously welded to the surface of the equipment and not attached via drilled and tapped holes.
Other factors like time, temperature, water, pH and nutrients also are factors that affect pathogenic growth niche development. Of these, the availability of water and nutrients are key factors for most growth niches on equipment. Through work by the American Meat Institute Foundation (AMIF) Listeria Intervention and Control Workshop, we also know that mid-shift cleanup and the use of high pressure during cleaning create high-risk situations. For example, we know that the same equipment located in different plants can produce slightly different product. The same is true in terms of the development of growth niches in equipment: The same equipment located in different areas can exhibit different levels of growth niches within a plant. Factors that may affect growth niche development include actions such as high pressure rinsing, build-up of product debris and excessive rinsing such as caused by sticky products. It is this rinsing process that is believed to be a significant way in which equipment can become impregnated with undesirable organisms.
If growth niches are not designed out of the process, then they must be managed by minimizing their contamination potential with process control techniques. Identifying the sanitation critical factors is the first step in this effort. First, the manufacturer should consider the degree to which equipment needs to be disassembled for effective cleaning and sanitizing. The chemical sanitizer treatment being used, including consideration of flood sanitation coverage and the requirements for treatment time and chemical concentration, is another significant factor that will have an impact on successful control of pathogenic growth niches. Whether the plant heat sanitizes the equipment--cooking machinery in an oven or smokehouse, covering equipment with a tarp and injecting localized steam, and/or placing items in a Clean-Out-of-Place (COP) tank--and how it conducts non-daily scheduled sanitation, such as rotational deep cleaning of equipment or equipment pasteurization also are sanitation critical factors to be taken into account. Finally, effective GMPs after the flood sanitization step must be implemented to further assure that growth niches are managed.
The Seek & Destroy Process
As mentioned, the Seek & Destroy process can be used by food operations as a tool to investigate three important areas associated with the identification and control of Listeria monocytogenes in the plant environment: (1) positive result from the Listeria monitoring and control program; (2) equipment or process qualification; and (3) process validation. The accompanying flow chart details the Seek & Destroy process (Figure 1). As shown, the essence of the S&D process is to disassemble equipment and, during disassembly, to evaluate the equipment for growth niches, If growth niches are discovered during disassembly, a microbiological evaluation of those areas is conducted.
Investigation of a Positive Result. Upon receiving a positive result during monitoring, the first action by the S&D investigation team is to identify the scope or physical area where the investigation will occur. Next, the team assesses whether there has been any exposure of product to high risk situations. The AMIF Listeria Workshop has identified numerous practices or events as high risk. To control these situations, control measures need to be in place to address the high risk. Examples of high risk include the use of high pressure air or water, drain backup, movement of a packaging machine, and so on. If exposure has occurred, then process control program and monitoring records must be evaluated for that specific situation.
The next step is to conduct the S&D mission, performed on the equipment and in the areas within the scope of the investigation. There are four expected results that will transpire when using S&D as an investigation tool:
• Observation of excessive organic material buildup.
• Process control chart (log APC).
• Assessment of the sanitation process control system's critical factors.
• Identification of any pathogenic growth niches.
The S&D team's mission is to observe and evaluate the normal cleaning and sanitation steps of the sanitation cycle. Next, the team monitors to assure that all equipment pieces and components requiring heat sanitization are adequately pasteurized. The team will observe the assembly, and then observe the post-assembly sanitizer application. Again, the goal is to make sure that all parts are effectively cleaned and sanitized, such that if there is any recontamination during the normal assembly activities those parts are covered with a spot sanitizer application. During these events, the team also is monitoring to make sure that GMPs are being followed. At this point, the equipment is assembled and set up to start running product.
The next phase of the S&D mission begins when the team stops the operation just prior to product coming to the line. Next, the equipment is disassembled back to its normal daily sanitation level of disassembly. As the equipment is being disassembled, the investigation team is looking for any questionable areas and conducting environmental hygiene swabbing and sampling to identify levels of microbiological activity. Once the equipment is disassembled to its normal daily level, it is disassembled completely, and again, as the disassembly process continues, the subsequently questionable areas are evaluated and swabbed. The key to this process is to completely take the equipment apart, and as disassembly proceeds, monitor for any level of unacceptable organic buildup. If unacceptable organic buildup is found, then one of two things must be addressed: Either the degree of disassembly was not appropriate or the cleaning methods were not acceptable.
Microbiological evaluation of the equipment also is an important part of the S&D approach. Obviously, if Listeria is found during the S&D mission, a pathogenic growth niche potentially exists. However, the investigation team may growth as measured by APC in these niches, as well. If this is the case, the team can monitor the APC result and develop a process control chart of the log of the APC growth. In this manner, any out-of-control points will be identified as growth niches requiring control.
Equipment or Process Qualification. Effectively qualifying equipment and processes is very important to the food manufacturing operation, and the S&D process can be used to good effect in this area. Installation qualification, for example, establishes confidence that process equipment and ancillary systems are capable of consistently operating within established limits and tolerances. Process performance qualification establishes confidence that the process is effective and reproducible, and product performance qualification establishes confidence through appropriate testing that the finished product produced by a specified process meets all release requirements for functionality and safety. Thus, when an operation introduces new equipment to the line it must be qualified for that process. This includes equipment that is new, that has been brought out of storage, that is used, or that is new to a high-risk process. The latter three situations are identified in the AMIF Listeria Interven-tion and Control Workshop as high risk because biofilm that is protected or embedded in growth niches have a great potential to contaminate the environment or product.
The results expected by virtue of using S&D as a qualification tool, specifically as it pertains to microbiological equipment qualification, are:
• Observation of excessive organic buildup.
• A measure of the potential for an area to support pathogenic growth (i.e., process control chart, defines areas needing redesign, and addresses areas that need to be managed via sanitation critical control factor).
• Identification of any pathogenic growth niches.
As part of applying S&D to the equipment qualification process, manufacturers should review the AMI Equipment Design Taskforce's 10 Princ-iples of Sanitary Design (Table 1). These principles are used as an evaluation template to help the S&D investigation team identify equipment design problems. These sanitary design principles, coupled with the S&D approach, provide an integrated tool to help qualify each piece of equipment. Based on these 10 principles, the AMI Task Force also has designed a 78-point checklist, which serves as an additional tool to evaluate equipment design (www.meatami.com).
As shown in Figure 2 from the AMI Equipment Task Force, all equipment is reviewed and accepted by the facility, through its own or a third-party review, prior to installation in the plant and the application of S&D to the qualification process. To be effectively evaluated, the equipment must be used in the processing line for a 90-day period. Following that period, S&D is applied: The equipment is disassembled to its normal daily level and then evaluated both visually and microbiologically as it is completely taken apart. This is an ideal time for the equipment manufacturers' representatives to be on hand, so they can see how their design performs in the real world. It is at this step where S&D really tells the manufacturer how effectively a piece of equipment has been designed for sanitary purposes.
Process Validation. This is the third area for which S&D provides valuable information to the processor. Process validation is critical to our knowledge and, ultimately, to the successful control of pathogens like Listeria monocytogenes. How do we know that the sanitation process is really effective? Is it one month of negative contact surface results? Three months of negatives? A year's worth? In other words, what really constitutes a validated process? Validation is simply a tool or procedure that enables processes to be more predictable. Predictability is one of the greatest challenges to the management of this environmental pathogen, because we know that control via product testing is like playing a game of Russian roulette.
S&D, used in conjunction with in-process effect measurements, can provide greater insight into the process by measuring and assessing the critical factors of the sanitation process, and by identifying a problem before product and consumers are placed at risk. The U.S. Food and Drug Administration's (FDA) definition gives us a clear definition: "Process validation is establishing documented evidence which provides a high degree of assurance that a specific process will consistently produce a product meeting its determined specifications and quality characteristics" (www.fda.gov/cder/guidance/pv.htm). Validation is an essential element in the establishment and implementation of a process procedure, as well as in determining what process controls are required in order to assure conformance to specifications. Again, microbiological safety must be designed and built into the process, since microbiological quality cannot be inspected or tested into finished product. Successfully validating a process may reduce the dependence on more intensive in-process and finished product testing.
Used as a process validation tool, S&D allows the evaluation of any excessive organic buildup, as well as the evaluation of the process control chart (log APC) to help determine whether there are any pathogenic growth niches in the process. If growth niches are uncovered, the manufacturer has the necessary information to get those growth niches under control.
Committed to Control
The Seek & Destroy process is a tool that when properly applied can provide the manufacturer with insight about the microbiological operating characteristics of a high-risk production process. As food processors, we know that the greatest fear is being the cause of a foodborne illness outbreak, having unsafe food. S&D offers a science-based and systematic approach with which we can manage, control and eliminate growth niches.
John Butts, Ph.D., is Vice President, Research, with Land O'Frost, a producer of premium lunchmeat products and ingredients for retail, food service and industrial customers. Butts is active in various AMI committees and task forces, including 25 years with the Scientific Affairs Committee on which he currently serves as chair. He also serves on the Meat Inspection Committee and is on the AMI Board of Directors. Butts has been a team member who has helped develop and teach the AMIF Listeria Intervention and Control Workshops. Contact him at firstname.lastname@example.org.Categories: Contamination Control: Microbiological; Facilities: Sanitation, Hygienic Equipment Design; Food Types: Meat/Poultry; Process Control: Process Validation; Regulatory: Guidelines; Sanitation: Cleaners/Sanitizers, Environmental Monitoring