The threat within

DuPont Qualicon’s Doris Engesser-Sudlow explains the importance of controlling Listeria and how food companies can face the challenge in an effective way.

“Because of its widespread presence and unique survival abilities, Listeria is a severe problem for food-processing environments that deal with the preparation of ready-to-eat foods”
-Doris Engesser-Sudlow, DuPont Qualicon

Listeria is an environmentally widespread bacterium that exists naturally in soil and water as well as in a variety of mammals, avian species, and fish. Its presence can affect a wide variety of the processed foods we consume daily from dairy and meat products to fish and vegetables.

Of six Listeria species, only Listeria monocytogenesis is infectious for humans. It is one of the most harmful food-borne pathogens, with 20 percent of clinical infections resulting in death. For most healthy young and middle-aged people, chances of severe illness are low, with typically mild, flu-like symptoms or gastroenteritis. But in vulnerable groups that include pregnant women, infants, the elderly and other people with compromised immune systems, the consequences can be very serious and sometimes fatal.

Listeria has a unique capacity to survive and grow in hardy conditions such as very low temperatures. It thrives in normal refrigeration conditions and can survive freezing, although it is eliminated through cooking at high temperatures. It also has the tendency to form highly resistant layers of bacteria known as biofilms, which can be difficult to remove through cleaning.

Because of its widespread presence and unique survival abilities, Listeria is a severe problem for food-processing environments that deal with the preparation of ready-to-eat (RTE) foods. Food retailers sell these foods ready for consumption without the need for cooking or reheating. The highest prevalence of Listeria can be found in RTE foods such as unpasteurised cheeses, deli meats and smoked fish.

Preventing outbreaks

Outbreaks of Listeria continue to cause heavy damage. In late 2008, an outbreak of Listeria in a Maple Leaf Foods plant in Canada killed 22 people and caused 57 other food poisoning cases. The bacteria travelled through deli meat products, found to be contaminated in the packaging area. Between 1991 and 2002, 18 outbreaks of invasive listeriosis were reported in Europe and they continue to occur frequently. 

Contaminated products not only cause a heavy economic loss due to potential food recall, plant closure for sanitisation and large delays, it can also have a significant negative impact on the company's reputation and brand.

European regulations specify that RTE foods must remain below 100 colony-forming units per gram (cfu/g) throughout the product's shelf life. High-risk RTE foods shown to support the growth of Listeria have an additional criteria of testing negative for Listeria monocytogenes in 25 grams of sample before leaving the factory. RTE foods for infants and special medical purposes must remain negative for Listeria monocytogenes throughout the product's shelf life. Environmental sampling for Listeria testing on surfaces is also a mandatory part of plant verification. 

High quality tools ensure success

In an industry that is facing ever-increasing pressures to produce and deliver high volumes of food in very short times, the chances of contamination problems are increasing. Providing high accuracy and sensitivity along with fast time to results, the DuPont Qualicon BAX System is a molecular method for microbial detection, offering new Listeria solutions for food and environmental testing as well as a broad range of other pathogen testing capabilities. When integrated into a plants' workflow, its shorter time to result compared to traditional methods as well as its high accuracy allows for faster response to the presence of pathogens, along with reduced expenses related to storage and inventories.

The problem of Listeria will continue to be a major issue for many food-processing environments and for RTE foods. A properly implemented safety protocol for sample testing, sanitisation and monitoring can significantly reduce the risk of outbreaks. Tools such as the BAX System, integrated into the production workflow, can help ensure that safe, high quality food products are the only ones that reach the consumer.

Doris Engesser-Sudlow is Business Director at DuPont Qualicon EMEA. DuPont Qualicon is a world leader in providing innovative, science-based diagnostic products that can reduce the impact of pathogens and other unwelcome organisms in food. For more information, please visit www.Qualicon.com.