Advancing quality assurance

Dr Berwyn Clarke discusses how new insights explain the presence of mycobacteria in retail milk.

Most consumers of dairy unquestioningly accept that pasteurisation provides a guarantee that products are safe to eat and drink. However, recent research using a new highly sensitive technology has revealed even more live mycobacteria exist in pasteurised milk than previously thought [1].

Live Mycobacterium avium subspecies paratuberculosis (MAP), which causes Johne’s disease in cattle and has been implicated in Crohn’s disease, were found in just over 10 per cent of the pasteurised milk samples that were tested across the East Midlands, UK. The prevalence of MAP is higher than previous studies have shown due to the higher sensitivity of the new phage-based technology that was used.

Johne’s disease, a chronic wasting disease of cattle and other ruminants, has a significant economic impact on the dairy industry. There is also a growing body of research that implicates MAP in the development of Crohn’s disease in humans [2]. Although no causal relationship between MAP and Crohn’s has been established, the dairy industry recognises that limiting human exposure to MAP would be sensible on a precautionary principle [3].

Earlier this year, milk buyers, such as the Tesco Sustainable Dairy Group, announced they would be delisting suppliers who are not engaged with Johne’s control plans.


Within dairy production, quality control procedures to better monitor the levels of MAP in pasteurised milk have been difficult, as these mycobacteria are extremely slow growing. Culturing these bacteria takes several weeks to determine if any MAP have survived a food safety or control process.

Yet the new phage-based detection method, which was used within the research due to be published in the Elsevier Journal of Food Microbiology later this year [1], allowed experiments to be performed quickly – providing the insight dairy producers and processors need to further improve control measures.

The highly sensitive and specific Actiphage assay, which is commercially available, uses a virus (bacteriophage) that can only replicate in viable MAP cells. Within hours, the virus breaks open the MAP cells, releasing DNA, which can be used to confirm that MAP is present.

New processing methods

Contrary to previous hypothesis, the research also revealed that MAP does not enter the milk due to faecal contamination, but via somatic cells within the udder. This intracellular location may help explain how the mycobacteria are protected against heat inactivation during pasteurisation and could lead to new processing methods to ensure the mycobacteria are inactivated.

With consumers increasingly aware about the impact of food and drink on their health, the phage-based assay provides a powerful new tool to help producers and processors rapidly test milk, milk formula and other dairy products as part of quality assurance programmes – enabling the dairy sector to stay one step ahead of consumer demand.


Dr Berwyn Clarke is chief executive at PBD Biotech.

References are available on request.

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