New draft guidelines released this January by the U.S. Food and Drug Administration (FDA) give a clear overview of measures that food industry members dealing with ready-to-eat (RTE) foodstuffs can take to combat product contamination with Listeria monocytogenes.1 Although non-binding and not for implementation, producers would be wise to take heed of the draft since it combines industry best practices with Food Safety and Inspection Service protocols in a robust document for foodborne disease (FBD) pathogen management.
Listeria species are bacteria that are ubiquitous in the environment. The main pathogen in this group for causing human FBD is L. monocytogenes. Infection is usually by ingestion of contaminated foodstuffs, and the usual outcome is a mild and self-limiting febrile disease with gastrointestinal symptoms. However, in elderly people, pregnant women and those with compromised immune systems, the disease can be much more serious. In these cases, infection can be fatal, causing fetal death and miscarriage, and systemic disease.
RTE foods are a prime source of listeria since they are usually minimally prepared once in the hands of the consumer. Meal items such as salads, shellfish and soft cheeses do not usually undergo high temperatures in order to prepare them for the table. Moreover, since Listeria microbes are highly resistant to many standard food practices, they can thrive and indeed multiply under refrigeration. They also survive freezing for short periods, being viable on thawing.
Since they are widespread in the environment, Listeria control measures emphasized in the draft guidelines aim to minimize contamination from external sources during manufacturing of RTE products. These sources include personnel, equipment and production environment, during packaging, storage and transport.
The guidelines offer comprehensive advice with step-by-step protocols for minimizing and preventing contamination at all stages of the industry cycle. They are aimed at producers including manufacturers, processors, packagers and those who hold RTE products prior to consumer purchase, already under regulation by the Code of Federal Regulations, Title 21, Part 117: Current Good Manufacturing Practice, Hazard Analysis, and Risk-Based Preventive Controls for Human Food. Furthermore, the draft complies with the FDA Food Safety Modernization Act.
The FDA advisers recommend control of foodborne listeriosis by concentrating on preventing contamination. The guidelines cover detailed actions that food producers should take under the following broad headings:
- Plant design, construction and operation
- Design, construction and maintenance of equipment
- Personnel and staff measures
- Sanitation and water services
- Ingredient controls and final product design
- Storage and transportation
- Listericidal process control and monitoring
- Environmental monitoring and RTE product-testing procedures
Advisory actions include segregating RTE workers from those involved in raw product preparation and providing designated protective clothing, employing water supply and drainage service that avoids aerosolizing liquids near RTE foods, using listericidal agents such as sorbic acid, reducing water content and pH to levels inhospitable to Listeria species and ensuring efficient equipment operation that prevents build-up of product residue.
The guidelines also advise regular monitoring for microbial presence in the environment as well as regular product testing. They stipulate that a recognized and approved testing method should be used, such as the SureTect™ Listeria monocytogenes PCR Assay (Thermo Fisher Scientific), which has been thoroughly evaluated in a variety of relevant food matrices and environmental samples. This molecular tool is AOAC-RI and NF VALIDATION certified and can handle rapid detection in a variety of complex foodstuffs and environmental samples with accuracy.
Although the main FBD pathogen of interest is L. monocytogenes, regular and comprehensive testing for all Listeria species will flag cleanliness and sanitation concerns in the production environment in a timely manner. It is also important, however, to test product regularly for the pathogen itself, and the guidelines set out a workflow for dealing with positive identification during routine testing.
In summary, although the guidelines are not subject to regulation in the United States, food industry members involved in the RTE environment should read the advice closely. The emphasis on regular testing using approved methods is vital to preventing contamination and avoiding potentially disastrous product recalls that will harm consumers and disrupt brand loyalty.
Learn more about testing for Listeria in our food and beverage community.
1. U.S. Food and Drug Administration (2017) “Draft guidance for industry: Control of Listeria monocytogenes in ready-to-eat foods.”