Bacteria are cultivated to find out how they live and reproduce. Photo: Siri Elise Dybdal © Nofima

Project Year 2017

How food bacteria survive

 Food safety and quality  

Bacteria work together to form highly resistant biofilms, which cause problems in food production. Scientists from Nofima have been looking at what can be done.

Micro-organisms can undermine food quality and food safety. Dangerous bacteria such as Listeria cause serious illness, while spoilage bacteria reduce the shelf life of food.

These bacteria are found throughout the food chain from producer to consumer and thrive on surfaces such as factory conveyor belts. Different types of bacteria can also stick together, to form slimy communities called biofilms. Bacterial biofilms are especially problematic because they are often more resilient than single bacteria. Biofilms are not as easily removed by rinsing, disinfection and washing because the bacteria collaborate and the products are not able to penetrate the film. Biofilms also often develop in places that are hard to reach.

Nofima scientists have investigated how bacteria like Listeria are able to establish themselves and survive on surfaces – and what can be done to make it harder for bacteria to hide. For example, they have looked at disinfection of production belts in the food industry.

A growing problem

Listeria bacteria are common in nature and can enter the food production chain with raw materials and people.

“Listeria is a growing problem and very serious for people with weakened immune systems and the elderly. At the European level, we are seeing a rise in the number of cases of listeriosis, which is thought to be related to higher life expectancy and changes in eating habits,” says scientist Annette Fagerlund.

“In order to simulate the disinfection process in food production, we made a model, allowing us to study this in more detail,” says Solveig Langsrud, senior scientist at Nofima. She explains that the scientists consulted industrial actors in the planning stage, to ensure the studies were realistic.

Bacteria hide

The study found that washing and disinfectants kill quite a few bacteria, but unfortunately they often grow back quickly.

“They appear to be gone when you test right away. But all you need is a single bacterium, and they are off again. They grow back over night. The bacteria that survive in the production environment over time seem to be good at attaching themselves to surfaces and better at withstanding the cold,” Langsrud explains, adding that it is especially bacteria that grow in biofilm that survive.

“One problem is that while the top surface of, say, a conveyor belt is made of a smooth material, the underside is often made of another material that is harder to clean. And bacteria hiding on the underside can easily come over to the topside during food production. For example, bacteria can hide in threads on the underside. One solution might be belts that are smooth on both sides,” says Fagerlund.

Other places the bacteria hide are screw holes. Previous studies have found that Listeria bacteria can remain in equipment for years. They can get down into a crack and stay there.

Wear and tear

Scratches on equipment caused by wear can also harbour bacteria, meaning it is important to keep equipment in good condition.

“Instead of looking for bacteria, the focus should be on looking for places where bacteria can hide. Whenever possible, equipment should be chosen that does not have suitable hiding places. It is important to continue working to improve designs and cleaning agents,” says Langsrud.

The next step in the project is to study the cleaning agents in more detail.

“We have been contacted by detergent suppliers who want to develop cleaning agents that can remove biofilm, and we have devised a method that allows us to test efficacy here,” says Langsrud.

Tecnical Comitee for Laundry and Disinfectants to food industry (TKVND)

The Foundation for Research Levy on Agricultural Products (FFL) - research funds over the agricultural agreements

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