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Listeria monocytogenes (L. monocytogenes) is an environmental pathogen that can contaminate foods and cause a mild, non-invasive illness (listerial gastroenteritis) or a severe, invasive illness (listeriosis). Although the number of outbreaks and illnesses from this pathogen are not high compared with other pathogenic organisms, such as Salmonella, listeriosis is considered to be a significant foodborne pathogen since the illness outcome is severe and the fatality rate is high.

In light of recent notable outbreak incidents with foods such as caramel apples and ice cream, the publication of FDA’s draft guidance for L. monocytogenes in ready-to-eat (RTE) foods is timely. Control of the process environment is important to minimize potential cross contamination of RTE foods by this environmental pathogen. This draft guidance provides a comprehensive tool to help protect public health and reduce the incidence of listeriosis. The construct of the document is thorough and well laid-out. It is intended for the food manufacturer that is subject to the Food Safety Modernization Act (FSMA) and is required to follow current good manufacturing practices for human food of part 117 (CGMP – Subpart B) and/or the requirements for the hazard analysis and risk-based Preventive Controls for Human Food (PCHF) in 21 CFR 117 (PCHF).

The guidance identifies several examples of measures that could significantly minimize or prevent the contamination of RTE food with L. monocytogenes. This guidance is not intended for the food manufacturer of RTE food that receives a listericidal control measure applied in the final package or before packaging.

Lm SURVIVABILITY. Although temperatures below freezing can retard the growth of L. monocytogenes, the pathogen can slowly multiply at refrigeration temperatures. For this reason, refrigeration is less effective as a control measure for L. monocytogenes than it is for other foodborne pathogens. L. monocytogenes also can tolerate high salt concentrations, and survive frozen storage for extended periods. Moreover, listeriosis is largely associated with RTE foods, especially those that have intrinsic characteristics (pH and water activity) that support the growth of the pathogen. It is widespread in the environment (soil, water, sewage, decaying vegetation, etc.), and it can be readily isolated from humans, domestic animals, raw agricultural commodities, food packing, and processing environments (particularly cool damp areas). Additionally, L. monocytogenes has been shown to persist in equipment and the processing environment in harborage sites.

However, the application of CGMPs and PCHF requirements to the production of RTE foods can significantly minimize or prevent L. monocytogenes contamination of an RTE food through the control of raw materials or other ingredients, sanitation controls, sanitary equipment design, physical barriers, segregation of foods that have been cooked from those that have not, etc. Many of the recommendations of this guidance, which complements but does not supersede recommendations from other FDA guidance, are adapted from several scientific publications that provide detailed recommendations for the control of L. monocytogenes.

L. monocytogenes can multiply even at refrigeration temperatures.
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SIGNIFICANT ASPECTS. There are particular areas in the guidance that are worth noting, such as the example of potential corrective actions following a positive Listeria spp. test result on a food-contact surface (FCS). The example in the guidance, which is a notable change from the 2008 draft guidance, mirrors many aspects of the USDA Food Safety and Inspection Services (FSIS) recommendations on the same issue. The approach, known in the industry as “seek and destroy,” has been credited with reducing the presence of L. monocytogenes in meat and poultry establishment environments.

The guidance also encourages testing that is intended to find L. monocytogenes from environmental samples (and from product samples in certain incidences). A strong environmental testing program should seek out and find L. monocytogenes in the environment so that effective corrective actions can ensue. Therefore, the guidance encourages facilities to test for Listeria spp. in environmental sampling to increase the chance of finding possible harborage sites.

The guidance also encourages facilities to conduct comprehensive and robust testing, rather than punishing them for positive findings. Integrating these approaches, along with the food safety requirements under FSMA, should lead to more effective efforts to control L. monocytogenes in RTE products. RTE facilities that produce foods regulated by both USDA/FSIS and FDA also will benefit from a uniform federal approach to reducing the risk of environmental contamination with L. monocytogenes.

It is important to point out that the objectives of environmental monitoring programs are to:

  1. Verify the effectiveness of control programs for L. monocytogenes.
  2. Find any L. monocytogenes and harborage sites.
  3. Ensure corrective actions have eliminated L. monocytogenes and harborage sites when found in a plant.

FDA also states in the guidance that environmental monitoring procedures should be risk-based and should establish strategies based on the characteristics of the RTE food, the facility, the equipment, the processing methods used for those foods, the likelihood of product contamination, and the processing methods used for those foods. Under this approach, the greater the risk that an RTE food could become contaminated with and support the growth of L. monocytogenes, the greater the frequency of environmental sampling and testing and the more stringent the corrective actions should be.

The draft guidance is a well-written, comprehensive document intended to help the food industry minimize foodborne listeriosis incidents. As such, we expect the industry to eagerly await the final document that FDA will update based on submitted comments.

The GMA authors are Stone, senior director, science policy, compliance and inspection; Kataoka, scientist, science operations; and Martino, processing specialist, science operations.