In the world of the infinitely small, the struggle for survival is intense, and microorganisms are no exception. They too seek out favourable environments in which to protect themselves, feed and reproduce. To do this, they settle on different surfaces and proliferate on the basis of available moisture and nutrients.

At first, there are just a few microbial families, but over time the community will diversify and become more structured, forming what might be considered an actual "city of microbes." It protects itself by secreting sugars that create a sort of sticky barrier between itself and the outside environment.

This organized structure is called a biofilm and can be found in many different places, such as on rocks near a lake or on the surface of our teeth. Over time, biofilms develop to the point where fragments break off and can settle elsewhere and invade the area. Hence the importance of controlling their proliferation.

In dairy production and processing, the various surfaces in contact with milk are also conducive to the development of biofilms. Once established, these biofilms can become attractive habitats for undesirable bacteria or moulds, thus affecting the quality and safety of milk.

Paradoxically, biofilms can contribute to certain typical traits thanks to their level of adaptation to the surrounding environment. So, to maintain microbial harmony and balance, it becomes important to understand these dynamics in the milking system, the point at which milk enters production, and in the cheese-making process.

The composition of biofilms can vary at different stages of the milk's journey, influencing its taste, quality and technological processing properties. This variation reflects the importance of monitoring and managing the risks of microbiological contamination throughout the dairy production chain, where biofilms play a key role, potentially being both beneficial and harmful depending on the microorganisms they harbour.

The aim of our research project was to carry out a microbiological profiling of the biofilms present at different places and times along milk’s journey from the farm to the cheese dairy. Like a census, our aim was to define the microbial species that make up these biofilms. By exploiting advances in genetic analysis and using specialized computer tools, we were able to detect and quantify different types of microorganisms by analyzing their genetic signature in huge bioinformatics databases. The project was funded by the Dairy Research Cluster 3 under the Canadian Agricultural Partnership (Novalait, Dairy Farmers of Canada and Agriculture and Agri-Food Canada).

This study involved visiting over 50 dairy farms in Quebec and Ontario on two occasions during different seasons. Our aim was to find out whether microorganisms would be present in the nooks and crannies of the various milking systems, both conventional and automated, by taking samples just after washing. At the same time, samples were collected from small and large cheese factories on various surfaces in contact with milk. The aim was to determine the origin of the microbial components, by describing the diversity of strains that can be found in milk and cheese.

We observed the persistence of biofilms composed of bacteria, yeasts and moulds in the milking system after washing, with the diversity of microbial communities varying according to the farm, the location in the milking system and even the season when the sample was taken. Surfaces in contact with raw milk had a higher microbial load. Although food-borne pathogens can co-exist, their incidence was low. It is important to bear in mind that these biofilms do not automatically represent a danger, as many of these strains occur naturally in milk and can be beneficial for cheese processing.

In summary, our studies carried out on farms in Quebec and Ontario revealed that the milk pipeline and the long tube were the areas with the highest bacterial and fungal load in conventional milking systems, while the brushes and cleaning cups were the areas with the most microorganisms in automated systems.

The presence of several microbial species in the same place is an indication of the richness of the diversity. This diversity also varies between the same pieces of equipment from different farms, probably due to variations from the animals or the farm environment. Differences in the microbial diversity associated with raw milk from the reservoir were also observed in all types of system, once again demonstrating the great variability of biofilms between farms. On farms where the milk was processed on-site, we observed the same places where the most biofilms were found, i.e., the farm's milk pipeline and the cheese dairy's ripening room.

In short, our research highlights the presence of biofilms in milking systems. We observed significant variability in the composition and distribution of biofilms, which highlights the need to manage microbiological contamination throughout the milk production chain. Particular attention to frequent cleaning and visual inspection of components to remove milk residues, by brushing or replacing parts, is therefore recommended. The microbial mapping of biofilms developed in this project can be used as a basis for ensuring that the microbial balance is maintained to guarantee high-quality milk and processed products. By integrating these results, we can develop targeted strategies to control biofilms, thereby improving the safety and quality of dairy products.

Observations on biofilms on dairy farms

• On dairy farms, the bacterial load of biofilms was highest on hard-to-reach surfaces.
• The structure of the multispecies biofilms varied significantly from one piece of equipment to another throughout the milking process, and the seasons were an important factor in the variation in composition.
• Great variability was detected between farms, and the microbial profile of biofilms was not the same in traditional milking systems as in automated systems.
• Dairy biofilms are dominated by proteobacteria, actinobacteria, lactic acid bacteria, yeasts and moulds.
• Surfaces in contact with raw milk appear to have biofilms with a higher microbial load.
• Food-borne pathogens can co-exist with the microbiota of a dairy biofilm, but their incidence is very low.
• The natural antimicrobials produced by lactic bacteria appeared to be promising molecules for combating biofilms.
• The prevention of milk residue build-up should be targeted to improve sanitation procedures.

This article was written by Evelyne Guévremont, Agriculture and Agri-Food Canada, Saint-Hyacinthe Research and Development Centre; Mérilie Gagnon and Denis Roy, Université Laval; Gisèle LaPointe, University of Guelph. 

Dairy Farmers of Canada (DFC) invests in scientific research to foster innovation in the Canadian dairy sector. DFC supports research initiatives that benefit all Canadian dairy farmers and works in collaboration with its members and other sector partners to address priorities outlined in the National Dairy Research Strategy. The goals of this strategy are to increase farm efficiency and sustainability, enhance animal health, care and welfare practices, and strengthen the role of dairy in human nutrition and health, as well as in sustainable diets. Visit DFC Dairy Research for more information.