Seafood Safety and Technology
Programs - Listeria Controls for Ready-to-Eat (RTE) Seafood


Listeria monocytogenes (Lm) is a food borne microbial pathogen that can grow under conditions that usually inhibit the growth of other pathogens such as temperatures as low as 34 degreeF and up to 10% water phase salt. Lm is widespread in the environment, and can be found in soil, water, sewage, and decaying vegetation. It can be readily isolated from humans, domestic animals, raw agricultural and fishery products, food processing environments, and the home.

Listeria Can Cause Serious Illness

Listeria monocytogenes can cause a serious disease called listeriosis, which primarily occurs when people eat foods contaminated with the organism. Healthy adults and children generally experience food borne illness symptoms and recover after a short period of time. However, certain populations such as pregnant women and their fetuses, infants, the elderly, and those with health conditions that suppress their immune system are much more susceptible to a severe form of this illness. In these groups, as many as 20 to 30% of the individuals who get listeriosis die. 

Listeria in Food

The organism can be found in a wide variety of foods, including meats, poultry, vegetables, dairy products, and seafood products. It has frequently been isolated from seafood products, and various studies conducted around the world have estimated an incidence level of 6-36% in cold smoked salmon and cooked fish and shellfish products. Foods implicated in outbreaks and sporadic cases almost always are refrigerated products that can support the growth of this organism. Under current US regulatory policy, L. monocytogenes is not acceptable at any level in RTE food products including seafood. Its presence in a wide variety of RTE food products has resulted in numerous product recalls and in many cases large economic losses.

Listeria in Processing Plants

Listeria monocytogenes survives extremely well in the processing plant environment. It may be introduced into plants through a variety of routes, including raw materials, employees’ shoes or clothes, and equipment. Lm also tends to form a biofilm to enhance its survival when resident populations become established in niches in the plant. These resident populations are not easily eliminated by general cleaning and sanitizing procedures.

Listeria Controls

Implementing an effective Listeria control program is a long-term commitment. Based on our current understanding, there are at least five key elements that need to be included in an effective Lm control program for RTE seafood products. These elements are: 1. Specific Sanitation and Good Manufacturing Practice (GMP) Controls, 2.Training of Plant Personnel, 3. Environmental Monitoring and Testing, 4. Refrigeration of finished products below 38 degrees F from production to consumption, and 5. Raw Material Controls.

Industry Assistance

NY Sea Grant’s Seafood Specialist, Ken Gall has collaborated with colleagues at Cornell University, other universities around the U.S., regulatory agencies national seafood industry trade associations, and individual firms that process smoked fish and other ready-to-eat seafood products to develop and evaluate effective control strategies for Listeria. The results of these efforts have been communicated to industry in workshops and invited presentations across the U.S., and many of the control strategies developed have been included in FDA’s 2008 “Guidance for Industry Control of Lm in Refrigerated Ready-To-Eat Foods."

Research and Outreach Collaboration

New York Sea Grant’s Seafood Specialist, Ken Gall, has collaborated with Dr. Martin Weidmann of Cornell’s Department of Food Science for over ten years to help producers of RTE seafood products such as smoked fish, crab meat, crawfish, cooked shrimp, seafood salads that will not be cooked before they are eaten to control the foodborne illness causing bacteria, Listeria monocytogenes.

Two New York Sea Grant funded projects designed to understand contamination patterns in smoked seafood operations in NY were conducted in the late 1990s. Following this initial work, Dr. Weidmann’s laboratory received over $1 million in funding support from the USDA/CSREES National Food Safety Competitive Research program to develop research and outreach activities to help producers of these products control Listeria. Collaborators were from the Universities of Delaware and Maryland, Virginia Tech, and Louisiana State University, the National Fisheries Institute and the National Food Processors Association.

For information on research, collaboration and outreach efforts with university and industry partners led to the development of a national Smoked Seafood Working Group, Listeria Control Manual (click here). Additional employee training programs focused on Listeria control are also available at this site.

Many of the suggestions outlined in this control manual have been included in the “Guidance for Industry on the Control of  Listeria monocytogenes in Refrigerated or Frozen Ready-to-Eat Foods” that was issued by FDA in 2008 (click here).

FDA is currently conducting a risk assessment for control options for Listeria monocytogenes in smoked fish, and expert consultations were provided by both Ken Gall and Dr. Weidmann in collaboration with the smoked seafood industry.


A series of five workshops on Listeria controls for processors RTE seafood products were conducted with the National Fisheries Institute and National Food Processors Association in 2003 in Louisiana, Virginia, New York, Seattle and Chicago. Invited presentations were given by Ken Gall to industry audiences in Seattle and Portland, OR in 2006 and at the International Smoked Fish Conference in Alaska in 2007. At least 500 firms across the U.S. have attended workshops or received educational materials or technical advice on Listeria controls.

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