Listeria

Listeria have been found on many different surfaces, and commonly in animals, soil, water, sewage, vegetation, vegetables and faeces. All types of raw food have the potential to be contaminated with Listeria, and some ‘ready-to-eat’ food products are of a concern.

Listeria is a problem in the food industry because eating food contaminated with some types of Listeria, e.g. Listeria monocytogenes, can cause illness and death.

Listeria are more successful in surviving harsh conditions than many other bacteria, as for example they can grow at refrigeration temperatures (< 4°C). Listeria are also able to grow and survive for long periods of time in biofilms and can thrive even in the sanitisers.

Being able to grow in biofilms helps Listeria stick to surfaces. Being in a biofilm also means they survive and transfer better. It protects them from drying out, heat and standard cleaning and disinfection chemicals. All of these traits contribute to how difficult it can be to control Listeria in the food industry.

In food production environments Listeria are typically found on floors, drains, food processing equipment, cleaning equipment, doors, chillers, freezers and air-handling systems.

The simplest way to control Listeria and prevent biofilm formation is through good, frequent cleaning and disinfection. It is essential to clean before disinfection. Cleaning is the physical removal of the contamination you can see, e.g. food waste. Cleaning removes most of the contamination and makes disinfection more effective. Disinfection then removes the contamination you can’t see, i.e., the biofilms of bacteria, including Listeria.

It is important to select cleaning activities that minimise the risk of spreading Listeria. Using a high-pressure hose can spread water droplets for meters and carry the Listeria you are trying to remove from one place to another.

Listeria are often found in damp and difficult-to-clean or inaccessible areas. Food factories should be designed to avoid these areas, and the equipment used in them should be hygienically designed. i.e., easy to clean. It is also important to maintain the buildings and equipment in a cleanable state.