Listeria - Why You Can’t Ignore the Risk

Unless you’ve been living off the grid you’re probably aware that Listeria monocytogenes is a hot topic in both mainstream and food industry news outlets. Listeria, one of the most deadly food pathogens, has been traditionally linked to contamination in deli meat and unpasteurized cheese products. However, in recent years, foodborne illness attributed to Listeria monocytogenes has increased significantly in the United States.

In the last two months alone, recalls reported to the FDA due to Listeria contamination have included bean sprouts, apple slices and dip, fresh pasta salad, frozen vegetables, ice cream products, smoothie kits, hummus, spinach dip, chopped spinach, and frozen ravioli. This opportunistic pathogen is a major concern in the food industry.

Not Your Average Foodborne Pathogen

Listeria is a very common bacteria that can be found almost anywhere in the environment including soil, water, and vegetation. It has been found on the surfaces of equipment, floors, drains, and walls. Unlike many other foodborne pathogens, Listeria can grow with or without oxygen, and can survive under low-oxygen conditions, even in the refrigerator. In fact, Listeria multiply better than all other bacteria at refrigerated temperatures, which are commonly used to control pathogens in foods. Freezing also has little detrimental effect on the microbe.

The Cost of a Recall

Before you start calculating how much a product recall must have cost those companies remember the primary purpose of a recall is always to protect consumers. Of course, there are other added benefits. They protect your company’s reputation. Recalls save your company from huge financial loss. And, they prevent harsh penalties from regulatory agencies.

The average cost of a recall to a food company is $10 million in direct costs, although the costs for larger brands may be significantly higher. Either way you look at it, recalls are expensive and carry a cost beyond dollars spent—a good argument for implementing comprehensive food safety plans and adequate control measures.

Control Strategies 

There are a few core strategies that will help control Listeria in your plant. It is important to understand and implement multiple control measures as no single step or intervention will be sufficient to eliminate or control Listeria risk in a given food processing environment. Food safety plans based on a good risk assessment are critical to help identify microbial risks and
potential management strategies.

Plant Design, Construction, and Operation

A good hygienic design and construction on an appropriate location is necessary to establish a sound microbial control program. It is important to separate areas where ready-to-eat foods are processed, exposed, and stored from areas where raw foods are processed, as well as from equipment washing areas, in-house microbiological laboratories, maintenance areas, waste storage areas, and toilets. Use of appropriate construction materials also plays an important role in minimizing cross-contamination. Food plants should be designed and constructed in a way that prevents standing water from accumulating in or around drains. Drains should also be easily accessible for proper cleaning.

Train Your Team

Further, it is critical to train every employee about the GMPs and Listeria preventive control measures to reduce potential contaminants from employee traffic and equipment. It is highly recommended that employees receive consistent training and that additional training is provided as needed to current and new employees on the GMPs for production, new equipment, environmental monitoring, and sanitary practices to ensure all are up to date.

Keeping Things Clean

In order to minimize and control Listeria contamination in a ready-to-eat food establishment, it is important to establish and implement a written sanitation standard operating procedure (SSOP) and sanitation maintenance schedule, which should be readily available to personnel responsible for cleaning, sanitizing, and monitoring. The written SSOP should address:

  • Time and frequency of cleaning
  • List of contact surfaces and equipment to be cleaned and associated dedicated brush/scrubber
  • Procedure to disassemble equipment if applicable
  • Time/temperature of cleaning solutions, concentration of cleaning compounds and sanitizers
  • Flow rate or pressure of cleaning solution
  • Procedures to clean soil and other debris from floors
  • Procedures to remove excess water from floors etc.

Sufficient care should be taken while assembling cleaned and sanitized equipment. For example, the equipment should not be placed directly on the floor. It is recommended to have two dedicated systems for cleaning equipment to process ready-to-eat and raw food products to avoid potential cross contamination. If separate clean-in-place systems are not available it is highly recommended that an alkaline cleaning solution at or above 160°F be used.

An Early Warning System

It is critical for the production of safe food products to monitor and collect environmental samples on both food-contact and nonfood-contact surfaces (e.g., drains) in a food manufacturing facility.

An environmental monitoring program (EMP) should be carefully designed after evaluating a facility and its products. An effectively implemented EMP will assess the overall hygiene program in a facility and provide necessary information to prevent possible microbial contamination of finished products.

The EMP provides valuable data (source and concentration) on indicator organisms in a timely manner so that an appropriate corrective action can be initiated. Many people have misconceptions about EMP. The EMP is not designed to validate the effectiveness of cleaning and sanitizing methods, but is more focused on validating cleaning and sanitizing frequencies, and other Good Manufacturing Practices (21 CFR).

For Listeria monocytogenes, the environmental monitoring program should focus on an indicator organism such as the nonpathogenic Listeria spp. which is more easily detectable than a target pathogen. If the EMP results indicate a trend toward an increased incidence of Listeria spp., then plant management should investigate to determine the reason(s) for the increase and subsequently take appropriate corrective actions to reduce or eliminate Listeria spp. Additionally, food-contact surfaces may be sampled routinely for Listeria spp. to
verify effectiveness of preventive controls. An effectively implemented EMP will act as
an early warning system for Listeria spp. or L. monocytogenes in both the production
and post-production environment.

Some common components that should be included in an EMP program include: an environmental monitoring team, zoning concepts, sampling time and frequency, selection of indicator or pathogenic microorganisms, sampling tools, labeling and shipping, baseline/target levels, trends and corrective actions, and mapping.

More Pieces to the Puzzle

Despite improvements in production, handling, and distribution of food products in recent years, protecting consumers from listeriosis remains a challenge. An effective pest control program must be implemented throughout the processing facility to eliminate potential pests that may act as potential vectors for a variety of bacterial pathogens including Listeria

A process validation or kill-step validation intended to deliver some degree of lethality is important to achieve food safety. The success of any Listeria control program depends on an effective HACCP/HARPC plan, a good hygienic design, cGMPs, sanitation program, employee hygiene practices, pest control program, an EMP, and good hygiene post-process handling procedures.

A Manageable Threat 

While Listeria remains a persistent challenge to food safety, arming yourself and your team with the facts and implementing solid control measures can go a long way toward mitigating risks to consumers and reducing your chances of a costly recall.

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