Listeria continues to make headlines and cause death, hospitalizations, and numerous food recalls. According to the U.S. Food and Drug Administration (FDA), there have been 16 different recalls since March of this year due to Listeria found in food products including hummus, frozen spinach, smoothie kits, and most notably ice cream.
What is unusual about Listeria bacteria is that they can grow and multiply under refrigerated conditions. Therefore, they can be present in cold, wet environments as commonly found in many packaging areas. Listeria niches have been detected in drains and areas of condensation within a plant, such as the ceiling or light fixtures. Listeria monocytogenes has contaminated ready-to-eat deli meats and hot dogs, refrigerated meat spreads, unpasteurized milk and dairy products, soft cheese made with unpasteurized milk, refrigerated smoked seafood, cantaloupes, coleslaw, and raw sprouts.
A Listeria contamination in ice cream is rare because the pasteurization process kills the pathogen. However, the bacteria may survive in the environment if proper sanitation procedures are not in place. Another possible source of Listeria contamination in ice cream may be the inclusions (candy pieces, chocolate chunks, etc.) that are put in after the milk is pasteurized.
It is very important for food processors to conduct regular environmental sampling for generic Listeria species in their plants. The frequency of sampling depends on a company’s size, previous history, and product properties. The driving force should be to try to find Listeria if present. In its “Guidance for Industry: Control of Listeria monocytogenes in Refrigerated or Frozen Ready-To-Eat Foods” the FDA recommends testing a minimum of five sites from critical food contact surface areas at least once a week and five from non-food-contact surface areas at least once every two weeks. It is not uncommon for the FDA to collect 100–300 environmental samples during an inspection.
If sampling reveals the presence of Listeria species, it is important that the processor immediately shuts down the plant and implements an aggressive sanitation protocol and resampling until Listeria is not found. Also, it is necessary at this point to test finished product for L. monocytogenes and, if found, initiate an immediate recall. Some major outbreaks of listeriosis have occurred because management has failed to take action when environmental samples indicated presence of Listeria.
As the Food Safety Modernization Act (FSMA) regulations are being finalized, I hope that the FDA considers a Listeria rule similar to the one enforced by the U.S. Dept. of Agriculture’s Food Safety and Inspection Service, which provides meat plants producing ready-to-eat products with three alternatives to control Listeria under a HACCP plan. These cover environmental and/or product sampling, post lethality treatment, and use of additives.
Fadi Aramouni, extension specialist and professor of food science
Elizabeth Clark, MS food science student
Kansas State University