A sticky layer of bacteria that attaches to surfaces such as equipment and drains, protecting the microbes from cleaning and sanitising.
A sticky layer of bacteria that attaches to surfaces such as equipment and drains, protecting the microbes from cleaning and sanitising. A biofilm is a community of bacteria that has attached itself to a surface and surrounded itself with a self-produced slimy matrix. Once bacteria settle on a moist surface and start to multiply, they excrete this protective layer, which anchors them in place and shields them from disinfectants, sanitisers and physical scrubbing. Biofilms commonly form on food-contact equipment, cutting boards, conveyor belts, drains, taps, hoses and anywhere water and food residue linger. The problem for food safety is that bacteria inside a biofilm are far harder to kill than free-floating cells, so a surface can look clean while still harbouring pathogens such as Listeria monocytogenes. Fragments of the biofilm can break off and contaminate food that later touches the surface. Because they build up gradually, biofilms are easy to overlook until routine sanitising stops working and swab results start showing persistent contamination. Australian food businesses control biofilms through thorough cleaning followed by sanitising, in that order, because sanitiser cannot penetrate a layer of food soil or an established biofilm. The practical routine is to remove visible debris, wash with detergent and physical action to disrupt the matrix, rinse, then apply a sanitiser at the correct concentration and contact time. Areas that stay wet, such as drains, sink undersides and the inside of ice machines, deserve extra attention because they are prime sites for biofilm growth. Under Standard 3.2.2 of the Food Standards Code, food-contact surfaces and equipment must be kept clean and in good condition, and this expectation covers hidden build-up as well as visible dirt. Businesses handling ready-to-eat foods, especially where Listeria is a concern, often use environmental swabbing to detect persistent contamination that signals a biofilm, then step up cleaning, dismantle equipment for deep cleaning, or replace worn surfaces that are too scratched to sanitise effectively. A smallgoods producer keeps returning positive Listeria swabs from a slicing machine despite daily sanitising. On inspection, a scratched plastic guard and a hard-to-reach hinge are found coated in a slimy film. The bacteria had established a biofilm that the routine wipe-down could not reach. Only after the machine is fully dismantled, scrubbed with detergent, rinsed and re-sanitised do the swabs come back clear.
Frequently asked questions
Why is a biofilm harder to clean than ordinary dirt?
The bacteria produce a slimy protective matrix that sticks them firmly to the surface and blocks sanitisers from reaching and killing the cells, so a quick wipe or spray on its own will not remove it.
Where do biofilms usually form in a food premises?
Moist spots that are not cleaned thoroughly are the usual sites, including drains, sink undersides, taps, hoses, ice machines, and scratched or worn food-contact surfaces on equipment.
Can a surface with a biofilm still look clean?
Yes. A biofilm can be invisible to the eye, which is why a surface may appear clean and dry yet still carry live bacteria that can contaminate food.
How do you remove a biofilm?
Clean first with detergent and physical scrubbing to break up the matrix, rinse, then apply sanitiser at the right strength and contact time. Badly scratched surfaces that cannot be sanitised should be replaced.
Which pathogen is most associated with biofilms in food premises?
Listeria monocytogenes is a common concern because it can survive in cool, damp environments and establish persistent biofilms in ready-to-eat food processing areas.
