Since garnering a high risk ranking in the U.S. Food and Drug Administration’s (FDA) “Quantitative Assessment of Relative Risk to Public Health from Foodborne Listeria monocytogenes Among Selected Categories of Ready-to-Eat Foods” report in 2003, smoked seafood products have been a focus of attention for food safety research. In a groundbreaking industry collaboration, a group of scientists with a grant to study Listeria patterns in 10 ready-to-eat (RTE) seafood facilities across the country and a working group focused on Listeria monocytogenes in smoked seafood plants spent the last several years exploring contamination patterns of the organism in an effort to track how Listeria moves around a facility and thus define prevention methods to block its path.

Ken Gall, a seafood specialist for the New York Sea Grant and Cornell Cooperative Extension at the State University of New York (SUNY) at Stony Brook, is a founding member of both groups. The original project team, which includes Dr. Martin Wiedmann, Cornell University; Virginia Scott, Food Products Association; Robert Collette of the National Fisheries Institute; Dr. George Flick, Virginia Tech; Tom Rippen, University of Maryland; Doris Hicks, University of Delaware; and Dr. Mike Moody, Louisiana State University, received funding through a U.S. Department of Agriculture’s (USDA) National Food Safety Initiative Grant to use molecular finger printing techniques with Listeria that would allow them to identify individual strains of Listeria and follow its movement patterns through RTE seafood plants.

During the three-year study, the group worked with four smoked seafood facilities, four crab meat facilities and two crawfish facilities. It spent the first year doing Listeria sampling throughout each plant, examining every step in the process, from raw material handling to packaging the finished product, to understand the individual ecologies of each environments and identify how Listeria behaved within them.

In the second year, the group used the collected data from the 10 plants to define specific control strategies to block Listeria’s movement in these environments. The plants then implemented those control strategies and tracked their results for six months, looking for changes in Listeria and commonalities in cause and effect among all of the plants.

In the third year, the group focused on outreach programs for the RTE seafood industry to let them know what they learned, what control strategies proved effective against the spread of Listeria, and how to implement realistic strategies in their own facilities.

The seafood study was guided by an offshoot of NFI’s Smoked Fish Committee, which became known as the Smoked Seafood Working Group (SSWG). SSWG has functioned as a forum to bring seafood experts from academia, NFI, FPA and processors of RTE smoked seafood together to have frank discussions about Listeria challenges, and to share experiences about what has worked, what hasn’t, and where the industry needs to go in the future to protect against Listeria contamination. The ultimate goal of SSWG was to create a Listeria Control Manual for Smoked Seafood facilities that identifies the elements of a complete Listeria control plan.

In July, SSWG responded to the U.S. Food and Drug Administration’s (FDA) request for information as it considers proposed rulemaking pertaining to risk assessment and control of Listeria monocytogenes in smoked seafood products. The document contained a literature review of Listeria monocytogenes research currently underway at several universities, remarks on current industry processing practices and Listeria control measures through the results of a survey of smoked seafood manufacturers, and details of steps to make smoked fish starting with raw product to the point of packaging.

Gall joined Food Safety Magazine to discuss the efforts of both groups and to share some surprising findings about how Listeria gets around in seafood plants and how it can be stopped.

FSM: It seems to me the most important thing to know about Listeria is how to destroy it. Why spend all this time and effort studying how it moves around?

Ken Gall:
Because of the danger of Listeria, you have to assume its ubiquitous in the environment and that the organism is always coming in. You can destroy it but because of its nature it will keep coming back. So, to prevent it from getting onto the finished product you have to be able to control it.

Before you can control Listeria in the plant you need to understand where the organism takes hold—where it may be living, where the niches are, and how it moves from a niche in one location across the plant to another niche. When you know that you can put barriers in place to prevent that movement.

FSM: What is molecular fingerprinting, and why is that an important part of tracking Listeria?

Molecular fingerprinting is used to identify the unique genetic subtypes of Listeria in the environment on in products, which gives us powerful information to determine how Listeria gets into a plant and what it does when it’s in there. Without the fingerprinting technique, you may be able to identify Listeria in four different areas of a facility, but you won’t know if it’s the same subtyppe of Listeria traveling throughout the plant or four unique subtypes all brought in from different locations. By conducting the molecular fingerprinting we were able to identify and track an individual subtype’s movement, which gave us evidence that a single strain was arriving in one part of the plant and moving from place to place.

Once we could say a particular subtype of Listeria was carried from one niche or location in the plant to the wheel on a cart to the floor in the finished product handling area, we could prove that certain activities in the plant were increasing the risk of Listeria contamination, then we could begin to devise control strategies to prevent its movement toward the finished product.

FSM: The grant to study Listeria came first. How did SSWG come about?

There’s always been a history of that sector of the seafood industry working together and collaborating. The two groups were created simultaneously and involved many of the same people. You could say SSWG was the merger of the original group and interested companies on NFI’s Smoked Fish Committee. SSWG included many of the same plants that were involved in the grant study, along with other industry experts, including members of NFI and FPA, and a number of additional processors of RTE seafood.

Everyone in this industry is dealing with Listeria, but there is no guidance on what works, what doesn’t or how we should prioritize improvements. SSWG’s goal was to identify the control strategies that worked and to produce a Listeria Control Manual for smoked seafood that identifies the elements of a complete Listeria control plan.

It’s rare to get that kind of synergy in an industry, where you build in science and real-world experience. We needed the collective wisdom, experience and science of the industry to make that happen, especially during the tracking year.

In the SSWG meetings we had frank discussions on what we knew and were learning about Listeria, what we still needed to learn based on industry experience, and what intervention and control strategies had or hadn’t worked for people in the past. We were able to test real-world strategies that had a chance of working, and we had industry experience behind us to look at what strategies would work and should be included in the manual. It was a beautiful collaboration. Each plant was very open about the things they had tried, whether they had worked or not. Some firms involved even had previous histories of recalls that they were willing to discuss. It was a great way to exchange ideas.

FSM: The initial grant was to study Listeria in all RTE seafood plants, but the working group focused specifically on smoked seafood facilities. Why was that?

Obviously, cross-contamination in any ready-to-eat facility is an important issue but the smoked seafood industry faces some specific challenges that make Listeria control even more difficult. Smoked seafood is in a high-risk category for several reasons: it’s not cooked or frozen; it has a high contamination rate because it’s processed in a wet environment with lots of traffic and multiple processing steps; it has a long shelf life, which gives organisms time to grow before the product is consumed; and because it is a high-cost product, consumers are less likely to throw away leftovers or product that is past its “use by” date. It’s all part of the equation for risk assessment.

FSM: The three-year program ended last year. What discoveries did the two groups make about Listeria in RTE seafood plants?

One of the most surprising things we discovered was that the industry was focusing on many of the wrong things. Our Year One data showed that the activities they thought were the highest risk for Listeria contamination, such as hand contact, were less of an issue than others problems they hadn’t even identified.

For example, smoked seafood may be processed in a wet environment, and the wetter the processing environment the more likely you are to have pathogens move from place to place. And, because smoked seafood processing requires many steps there is constant traffic in the plan –fish is wet brined, it’s moved to drying racks, then it is sliced and packaged–all of which adds to the risk.

When you have constant movement through a wet plant environment, people’s shoes and the wheels of the carts have an increased risk of tracking contamination from the raw side of the operation into the finished product handling area. In the smoked seafood industry, no one was focused on that, but our data showed that it is one of the biggest risk factors and that processors need to get control of that situation.

We also found that even though all of the plants were in the same industry, each one had a specific ecology, so while there were commonalities among the plants there were also unique aspects to each one. We’ve found over and over again that solutions for fighting Listeria have to be based on the unique needs of the plant, and that evaluating and testing the environment has to be done before you can implement effective control strategies.

FSM: What are some of the control strategies you found to be successful in blocking the transport of Listeria?

Some people think all they can do is build a new plant; it’s not true. You can spend a lot of money remodeling your plant but if inconsistencies in the way people work continue, you are still going to have same problem. One of most fundamental things you can do to control Listeria is get a hold of people management in the operation. Before you invest in new equipment or facility changes, you need to evaluate the way people move, and the flow of the process, and identify how that flow increases your contamination risk. That’s where the biggest problems occur. You have to design your system to minimize the possibility of the organism moving to the most sensitive areas of the plant.

To do that you need to take a fresh look at how the facility is laid out, how it is cleaned, and how people work within it. Sometimes a solution is as simple as rearranging a plant, moving equipment, eliminating wet mid-shift cleaning, or changing the roles of certain staff who move back and forth throughout the plant.

Sanitation is also key to Listeria control. Too many plants make sanitation an assignment at end of day that no one wants to do, but when it comes to Listeria you have to change that philosophy. The most effective way to do that is have a dedicated sanitation crew who do their job after everyone else is done.

Initially people resist these kinds of changes, but after a few months they will be amazed they ever did it any other way. They just need to understand and realize why their behavior is important and they need to know that they are not going to get away with doing things the old way. That’s the management part.

FSM: What if changes can’t be made to the way people move in facility or where the equipment is located?

If altering the layout or traffic in the plant isn’t feasible, then barriers need to be put in place to prevent the spread of Listeria. For example, you can designate dedicated equipment for certain areas, require mobile equipment to be cleaned and sanitized before it is moved into sensitive areas of the plant, and institute door foamers or spray barrier sanitizers on the floor as a mandatory walk-through sanitation barrier – we found these were better than foot baths, which are effective when used, however people tend to step over them to avoid getting their shoes wet.

In some cases older equipment, such as slicers that may have hidden harborages or are time-consuming and difficult to clean, should be replaced. This can be an expensive solution but you need to weigh the time and cost of breaking down and cleaning older tools against the capital investment in a better slicer that is easier and faster to clean.

Other solutions may require the complete elimination of certain high risk tools or materials, such as the stress relief floor mats used to prevent worker fatigue. We found those to be microenvironments full of niches for Listeria, and no matter what you do to clean them, even soaking them in pure sanitizer, doesn’t eliminate the problem. In most cases, facilities got rid of them.

The key for any facility is to first look at the process from beginning to end and identify the specific problem areas, then implement solutions that work for the environment, your time frame and your budget.

FSM: The final phase of the study was focused on outreach. How did that work?

Throughout the third year of the project we held day-long workshops inviting people from any RTE seafood plants to participate. A total of 170 individuals attended the five Listeria control workshops. Of these, 94 (56%) were from 62 different companies that process RTE seafood products. Industry attendees included 35 individuals from firms that process smoked fish, 33 from firms that process other RTE seafood, 14 from firms that process crawfish, and 12 from firms that process blue crab. A number of firms processed more than one type of RTE seafood products. Sixty of the attendees (35%) were from federal or state government agencies, and 16 attendees (9%) were from trade associations, universities, consulting or other service firms.

In the workshops, after going over what we already know about Listeria—the risk of recalls, regulatory policy, etc.—we discussed the data we collected, detailing where we found Listeria organisms in the plant environment, how it is likely to move around the plant, and how to build a Listeria control program in the plant. We reviewed where to start, how to study the flow of the facility, and how to evaluate a sanitation plan, and then outlined the biggest risk areas and the control strategies we’d found to be most successful and when they were appropriate.

Breaking down procedures step by step was very helpful for participants to break it down like this. We showed them how to evaluate what they are doing, and that it’s okay to implement changes in phases. The break-down process and prioritization gave them a way to organize their approach to Listeria control. Otherwise, the process can be too overwhelming.

FSM: What did workshop participants plan to do with what they learned?

At end of the workshops we surveyed participants to see whether they had controls in place prior to workshop, and based on what they had learned, what changes they planned to implement in the next six months. Of the 170 total participants, 111 returned surveys. Of those, 64 (58%) of surveys returned were from industry respondents. The feedback provided by the 64 industry attendees who returned a post-workshop evaluation form, indicated that two-thirds (43 of 64 attendees) had implemented some Listeria controls prior to attending the workshop and one-third (21 of 64) had not implemented any controls.

Overwhelmingly, we found that industry participants believe Listeria control is important, and the changes they intended to make generally were based on cost. Twenty-seven industry respondents (64%) said that sanitation training would be implemented in their plants immediately because they could see the immediate benefit and they knew it was doable. Less than half of the participants thought they could remodel the plant or buy new equipment in the next six months (Figure 1).

Of the 43 seafood manufacturing operations that had some Listeria controls in place prior to attending the workshop, 42 reported that they planned to change or enhance their existing controls after attending the workshop (Figure 2).

FSM: Have you followed up to see how many followed through on their plans?

Gall: We did. We went back after six months to see what they had done, and the most surprising thing we found was that 100 percent of participating plants had held employee training since the workshop (Figure 3). Now that they understand Listeria, they are spreading the word, and they are doing it in-house, with managers and supervisors as the trainers. That’s the best way to do it. Our workshop is great for owners and managers, but when you take it back to the workers they are more trusting when they hear the message from their own people.

In addition, more than 80 percent of those companies that modified or implemented new controls reported that they had made changes in their sanitation procedures (Figure 4). Other interesting results were that over 50 percent of the 21 firms that made changes in their Listeria control program also made changes in their Listeria testing program after attending the workshops, with eight starting environmental testing or changing frequency or sample locations; six starting to test finished products or changing testing procedures; and two starting to test raw materials. Five processors purchased new equipment that is easier to maintain and to clean and sanitize and three upgraded, remodeled or modified specific processing areas.

FSM: How can other people in the industry learn more about your work and apply it to their own Listeria control plans?

They can get a copy of the Listeria Control Manual for Smoked Seafood, which helps users identify the elements of a complete Listeria control plan that are critical to implement, including sanitation, handling controls and employee training, at As mentioned earlier, the SSWG identified at least five key elements that need to be included in an effective Listeria monocytogenes control program for RTE seafood products. These elements are:

1. Targeted GMPs and Sanitation Procedures for Listeria
2. Training of Plant Personnel
3. Environmental Listeria Monitoring and Testing
4. Raw Material Controls
5. Refrigeration of Finished Products (preferably below 38F [3C])

The manual was adopted by the national Association of Food and Drug Officials (AFDO) by reference in its GMPs for Cured, Salted and Smoked Fish Establishments as a way to control Listeria in the environment.

In addition, a copy of three employee training PowerPoint presentations developed for the Cornell University/ USDA project are available to download at, and a copy of the “Safe Food: It Depends on You” employee training guide and posters developed by the Universities of Delaware and Maryland is available at

FSM: What are you going to work on next?

Gall: We have begun a second study with Cornell University focusing on controlling Listeria in the most sensitive areas of the RTE smoked seafood plant where finished product is handled. We plan to go into much more detail about cross-contamination and how that occurs in that environment. Our goal is to build a mathematical model on how cross-contamination occurs in that area.

Understanding the relationship between behavior and the environment is the real challenge of controlling Listeria. We will continue to work on that for the good of the whole industry.