Food microbes that stick around

Embedded in their own slime, biofilms made from clusters of bacteria stick fast to surfaces in the food industry, posing potential hazards.

Cows grazing in front of a milking shed

Biofilms are slimy clusters of bacteria that cling to surfaces and cause significant problems in the food industry, including food spoilage and the risk of potentially serious illnesses such as listeria. They can be very hard to get rid of, as they are more resistant to sanitation processes than free-floating bacteria. The conditions in dairy factories are particularly favourable for the growth of biofilms made from heat-loving thermophilic bacteria stuck to stainless-steel surfaces, and biofilms are also a problem in other areas of food manufacture, such as the meat industry.

The Massey University Food Microbiology Biofilm Research Team, led by Professor Steve Flint and Dr Jon Palmer, is involved in a wide and interesting variety of projects that aim to help the food industry better understand and deal with biofilm issues. Professor Flint is Team Leader of Food Bioscience at Massey University’s Institute of Food Science and Technology, and Dr Palmer is a senior lecturer. Both have strong research interests in food safety and food microbiology.

Under the supervision of Professor Flint, Dr Palmer and other academic staff members, PhD student research features strongly in the work of the biofilm research team. In one project, student Sara Burgess studied a group of thermophilic bacteria from the dairy industry and found that several strains show genetic evidence of the ability to ferment lactose, the main carbohydrate in milk—a specific adaptation to their milky environment.

Interesting contrast

Professor Steve Flint (centre, front row) and members of the Food Microbiology Biofilm Research Team This result makes sense, given their home, but in an interesting contrast, fellow PhD student Siti Norbaizura Md Zain found strains of another dairy-related thermophilic bacteria which did not have the ability to ferment lactose, suggesting they were not genetically adapted to the dairy environment. How they can grow there without the ability to ferment lactose is an interesting question she is now exploring, looking at the interactions between these bacteria and another which can break down lactose, to see whether they behave synergistically to enable both to grow in a dairy system.

The team is also interested in how biofilm-forming bacteria get into the manufacturing process in the first place. Sometimes it is hard to identify the origin of food microorganisms, and this is particularly true in the dairy industry, because the thermophilic bacteria which colonise the surfaces of dairy manufacturing plants can be difficult to find in raw milk. But is this because they are not really there, or simply because they are hard to spot?

Dong Zhang has started a PhD project to profile the microbial content of raw milk throughout New Zealand using new genetic techniques to identify microorganisms which are usually difficult to find. This project will expand knowledge of the microbial composition of raw milk, perhaps shedding light on where some of the problematic bacteria are coming from.

Last year, the research team co-authored a book summarising 15 years of studies on biofilm development and control in the dairy industry. Biofilms in the Dairy Industry is a cornerstone for a better understanding of the current science and of ways to reduce the occurrence of biofilms associated with dairy manufacturing. Biofilms can also cause problems in other areas of food manufacturing, sometimes with the potential to cause serious illness. PhD student Jessika Norwak is investigating the genes involved in biofilm formation in different strains of the food-borne bacteria listeria, as well as their resistance to acid, heat and oxidative reagents. Identifying and understanding the genes involved in biofilm formation may lead to ways of lowering the risk of listeria contaminating food products.

In a related project, PhD student Shu Yan Wu is aiming to understand how listeria biofilms persist after antimicrobial treatment. And in another study of pathogenic biofilms, but this time in the meat industry, PhD student Haoran Wang has found calcium also plays a role in the biofilm development of Yersinia enterocolitica, a bacterium found in pork. So far, it seems that calcium may assist in forming the structure of biofilms, or may be involved in altering the properties of the bacterium to assist in attachment to surfaces.

Future work for the Food Microbiology Biofilm Research Team will focus on understanding the role of ions in biofilm development, and examining unusual spore-forming bacteria which are starting to appear in the food industry.

"Sometimes it is hard to identify the origin of food microorganisms. But is this because they are not really there, or simply because they are hard to spot?"

Research dates

  • Ongoing since 1996


Contact Professor Steve Flint

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