This portion of our website is devoted to keeping our customers and other interested parties abreast of our current research interests. Also, from time to time, we plan to use this site to express our opinion on issues that concern us as microbiologists involved in contamination control.

This Month's Topic: Foodborne Listeriosis

Listeria monocytogenes is a microorganism that has been of great concern to food producers in recent years. Unlike most foodborne pathogens, this organism is able to thrive at refrigeration temperatures as low as 0.5-3.0^oC (32.9-37.4^oF). Other resistant attributes of Listeria include the capability to withstand pH values from 4.1 to 9.6 as well as NaCl concentrations as high as 10%. It is because of this organism’s resistance to unfavorable environmental conditions, along with the serious illness that it can cause, that Listeria has become the feared foodborne pathogen of the present.

L. monocytogenes has been isolated from a variety of dairy and meat products including milk, cheese, and ready to eat meats. One of the most recent outbreaks of listeriosis involved a variety of hot dogs and deli meats produced at a single processing plant. The outbreak resulted in at least 100 illnesses that led to 15 deaths and 6 miscarriages or stillbirths.

Listeriosis, the disease associated with L. monocytogenes, is the most dangerous to newborns, pregnant women, and individuals who are immunocompromised. Healthy persons rarely develop this serious disease. Early symptoms can include fever, severe headache, and stiff neck followed by meningitis or septicemia. It is also believed that the dose of bacteria needed to trigger infection may be much lower than that required of other foodborne pathogens.

Within the food processing plant environment, Listeria is most likely to be isolated from drains, floors, walls, pools of liquid, and conveyors in both processing areas and coolers. These are primarily problem areas because they are usually wet and difficult to keep clean. In the above mentioned listeriosis outbreak, construction in the processing area appeared to be related to product contamination. While this process area was shut down, a large refrigerator unit was removed from the ceiling, cut into pieces due to its large size, and removed from the building. It is believed that this generated airborne dust particles contaminated with Listeria which ultimately contaminated production equipment.

There are several strategies that food processors can implement to reduce the possibility of Listeria contamination. The design and operation of a processing plant should not allow the entrance of animals, insects, or dust, nor should it allow raw product to cross-contaminate finished product. Food preservatives, such as potassium sorbate and sodium benzoate have been recommended to inhibit the growth of L. monocytogenes. Sanitation is also an extremely important component to the control of Listeria. A comprehensive cleaning and sanitation program must be established within the processing plant facility. Finally, food processors must have a complete quality assurance program that includes microbiological monitoring of the products as well as the environment.

At Biosan Laboratories, Inc., we offer a variety of microbiological testing services and products to support food processors in their endeavor to produce safe foods. Please contact Lesley Thomas at (800) 253-6800 x1229 or at lesley@biosan.com for additional information.

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Biosan Laboratories, Inc.
1950 Tobsal Court, Warren, MI 48091-1351
Phone (586) 755-8970 / (800) 253-6800
Fax (586) 755-8978 e-mail lesley@biosan.com