6 Gaps in Your Environmental Testing Program: #6 Biofilms

Biofilms can form on food processing equipment and are a frequent source of contamination. In this last installment of our series on 6 possible gaps in your environmental testing program, product manager Stefan Widmann discusses the danger of biofilms and how they can be detected.

What are biofilms?

Microorganisms are able to colonize surfaces by forming a polymeric matrix in which multiple microbial species may be present; this is known as a biofilm. Evidence shows that the ability to form and survive in biofilms is not restricted to specific groups of microorganisms. In fact, the vast majority of bacteria are able to form biofilms. Biofilms may therefore be composed either of monocultures or of several different microorganism species. Some researchers have suggested that the complex structure of mixed biofilms renders them more stable and more resistant to cleaning chemicals. The initial population that binds to the surface can change the properties of that surface, allowing for those that come later to adhere via cell-to-cell association; in some cases, the attachment of a second species may increase the stability of the biofilm population. For example, studies show that L. monocytogenes is more likely to adhere to steel in the presence of Pseudomonas.

Why should food producers care about biofilms?

Biofilms that form on food processing equipment and other food-contact surfaces act as a persistent source of contamination, threatening the overall quality and safety of food products and possibly resulting in foodborne diseases as well as economic losses. Spoilage microorganisms are known to be responsible for almost a third of losses in the food chain supply, making biofilm prevention and control a priority in the food industry. Microorganisms that form or thrive in biofilms are more resistant to disinfection, making them problematic in a wide range of food industries. Other effects of biofilms such as the corrosion of metal surfaces are a further critical concern in the food industries. In either case, the presence of biofilms in a food factory puts human health at risk. The degree of risk is dependent on the bacterial species forming this three-dimensional, living structure.

How can food producers detect biofilms?

The standard methods for detecting biofilms are still agar-media based. Surfaces can be sampled directly with dip-slides and contact plates or indirectly when using swab sticks, sponges or swab cloths. Indirect methods require that dilutions be prepared and spread out on petri dishes. In both direct and indirect methods, it takes days to get results. ATP test systems can provide faster results, but kinetic data from freely suspended planktonic cells should not be used as a reference for biofilm detection as the release of ATP is much lower for biofilms. Accordingly, ATP devices used to detect biofilms tend to have a much higher limit of detection, meaning that they are not as sensitive as they would be when detecting free floating bacteria. At the moment, there is no instantly secure way to detect biofilms before a production run begins. Direct cell counting technologies can help to close the gap as they can detect bacteria-forming biofilms instantly without the compromises that must be made to accommodate ATP systems.

This article originally appeared in International Food & Meat Topics 31 (6).