Ministry of Agriculture, Food and Rural Affairs

Biofilms in Milking Systems

Producers are often faced with sporadic spikes in their monthly Bactoscan counts. A high Bactoscan count one month and low count the next may indicate the presence of biofilms in the milking system.

So what are biofilms? Basically, they are layers of bacteria that are attached to milk contact surfaces and to one another with the help of slime (polysaccharides) that some bacteria produce. This slime traps other bacteria, debris and nutrients allowing the bacteria to reproduce protected from the effects of the wash cycle. Studies have shown that bacteria in the milk can attach themselves to a surface within 30 minutes, and within eight hours, a stable film develops. As the biofilms get thicker and thicker, they get harder and harder to remove. Gross biofilms may be visible as white-to-grey or cream-coloured deposits on milk contact surfaces or as a dullness to the sheen normally seen on stainless steel surfaces. However, biofilms can exist and cause problems even when not visible.

Biofilms are similar to the plaque that develops on our teeth or the slime on the rocks on the bottom of a stream. Once they are established in the milking system, pieces of the biofilms may break off during milking, resulting in sporadic high bulk tank Bactoscan counts. Any milk contact surface can harbour biofilms. They have been found on stainless steel, aluminum, glass, nylon materials, rubber parts, and Teflon seals. Improperly polished welds in pipelines, pinched gaskets and any milk contact surfaces that are scratched, cracked or pitted can foster the development of biofilms. Producers should assume that biofilms can form anywhere in the milking system.

Biofilm formation is not something that happens suddenly without warning. They most often develop when the cleaning and sanitizing program used in the milking system is not quite up to par. Producers should make sure that the water temperature used in the washing cycle meets the temperature suggested by the chemical supplier, that cleaner/sanitizer concentrations are correct and that the slugging action during the wash provides enough volume and force to clean the system adequately.

Thorough cleaning is the most important step in the prevention of biofilms. Cleaning prepares the milk contact surfaces for sanitizing. If the surface is not clean, it cannot be properly sanitized. Any remaining dirt or debris in the milking system can provide an excellent environment on which biofilms can easily develop. The application of sanitizers to dirty surfaces is both ineffective and a waste of money, as the ability of the sanitizer to destroy bacteria is drastically reduced. Once biofilms are established, they can be very difficult to eliminate. They act like insulators protecting the bacteria from contact with cleaners and sanitizers. They can actually shed water, and the bacteria in the biofilm can be much more resistant to sanitizers than bacterial cells floating around in the milk.

Since biofilms are very stable structures, the cleaning program has to be modified in order to remove them. Increasing the flow rate in the system, the chemical concentrations and the wash cycle times, (increases the contact time between the cleaners and the milk contact surfaces) may help to remove biofilms. Wash temperatures may be increased but raising them too high can cause proteins to "bake-on" making the biofilm problem even worse. The use of other cleaners that are better able to penetrate the biofilm protective barrier may have to be used as part of the milking system cleaning program.

Studies have shown that peroxyacetic acid-based compounds have the ability to penetrate and loosen the biofilm making it easier for the cleaners in the wash cycle to remove it. Use of a peroxyacetic acid cleaner/sanitizer in every wash cycle for two weeks will remove the biofilms. However, check with your chemical supplier before making any changes and always follow their advice.

The best defence against biofilms is making sure that the milking system is:

1. Well-maintained: gaskets and other plastic and rubber parts are replaced before they are etched or cracked. Spray balls are not plugged. Air injectors are working well.
2. Well designed: lines are self-draining and the welds are of sanitary quality. Also, the slugging action in the system provides sufficient fluid velocity for cleaning.
3. Clean: chemical supplier's instructions must always be followed. Temperatures, chemical concentrations and contact times are all critical in ensuring a clean system. Remember that all cleaning and sanitizing chemicals including peroxyacetic acid are hazardous and that appropriate protective gear must be worn when handling them.