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Biofilms : Secret colonies growing on your kitchen cutting boards?

Updated: Nov 1, 2021

The term biofilm may sound strange, but you have probably seen them more than you realize. The slime that grows in ice machines, the plaque that builds up on your teeth, and the SCOBY that starts kombucha are all biofilms. Some are helpful and some can be harmful.

So what exactly is a biofilm? It is a large number of bacteria which groups together and sticks to a surface, forming a colony. These bacteria in the colony are bound to each other in a thick substance that acts as a glue and forms a protective film. The picture below shows a biofilm that has grown on top of still water.

Kitchen cutting boards are a common place to find biofilms. Even if a cutting board looks clean, it may actually be growing a colony of bacteria in the scarred cutting board surface. You can not always see them, but if your cutting board feels slimy after washing, this is a clue that it may have a biofilm. If your cutting board has deep cuts or cracks, that will give a home for bacteria to live. In this photo below, you can see the discoloration which is a result of all the bacteria. Many bacteria that can cause foodborne illness form biofilms. Listeria, E.coli, and Salmonella have all been linked with biofilms.

Damaged cutting boards allow for bio-films to grow and multiply.

If these germs are on your cutting board, they can get in the food you serve and customers can get sick. For example, you may cut raw chicken on your cutting board early in the morning. You then place it in your sink to wash later. The cutting board sits until the middle of the day and in that time, a biofilm begins to form. When you wash the cutting board, you use your usual wash, rinse, sanitize procedure but because a biofilm has formed, not all of the bacteria wash off or are killed by the sanitizer. The bacteria continue to grow overnight. The next day, you use the cutting board to cut fresh lettuce. Some of the bacteria from the chicken can potentially transfer to the lettuce.

So what can we do? Here are some ideas to get you started.

Scrub the cutting board surface vigorously with soap and water before using the dishwasher or sanitizing.  Allow your cutting boards time to air-dry completely before putting them away. Biofilms thrive in moist environments. Replace deeply scratched or discolored cutting boards. Well-used cutting boards that have scratches and cuts on the surface can be the perfect place for biofilms to grow. The cuts on the board can harbor food and water, which helps the biofilm to grow. If your cutting board has scratches that are a different color than the rest of the board, it is time to replace it. Wash, rinse, and sanitize cutting boards every four hours when in continuous use. Cutting boards should be treated as an “in-use utensil”. This includes the cutting boards on your line. As always, follow the manufacturer’s directions regarding sanitizer. Use different cutting boards for raw vs. ready-to-eat proteins. For example, use a red cutting board for raw meat and a green cutting board for preparing vegetables. This greatly reduces the potential for cross-contamination.

Biofilms can form on many surfaces in your kitchen and once they are started, they can be difficult to remove. The colony protects the bacteria from chemicals, such as sanitizers. Studies have shown that biofilms can still be found on equipment even after it is washed, rinsed, and sanitized. This is concerning because bacteria can then transfer to the food you make. By being vigilant about preventing biofilms on food-contact surfaces and avoiding cross-contamination, you can minimize the risk of foodborne illness. Here is more about biofilms.

Update 11/1/21 : Article on Food Safety News

Fun fact: Sugary molecular strands (technically known as “extracellular polymeric substance” or EPS for short) hold the biofilm together. The image below shows a close-up view of a Listeria biofilm. The rod-shaped objects are the Listeria and the top arrow points to the EPS that holds the bacteria together. The EPS helps protect the bacteria from external threats - like your sanitizer!


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