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Reduction of Risk Associated with Contamination of Raw Milk by Mycobacterium Avium ssp. Paratuberculosis

Queen's University - Belfast
Hannah Research Institute
Start date
End date
The concern to the milk and milk products industry about Mycobacterium avium subsp. paratuberculosis (MAP) centres on its apparent heat resistance. There is a growing body of evidence that a proportion of the population of (MAP) found in milk survive pasteurisation at 72°C for 15 seconds. Thermal death information suggests that there is a sub-population of the organism, which owe their heat resistance to the formation of clumps. Bacteria buried in the clumps are believed to be protected and require additional heating to be inactivated. An alternate hypothesis advances the argument that, because the clumps contain up to 10,000 cells, it is anticipated that a proportion of the cells will survive. Despite the uncertainty surrounding the mechanism of apparent heat tolerance, the dairy industry has responded to the potential problem by extending the holding time of heat treatment of milk to 25-30 seconds (at 72°C). The likely success of the ad hoc response should be clarified.

The overall aim of the project is to evaluate processing combinations which could be used by the dairy industry to effect a 5-log reduction of MAP in milk. Studies will be conducted during the final stage of the investigation to determine the nature of bacterial clumping which has been shown to reduce the efficacy of heat treatment in the elimination of this bacterium.

This research will produce the first practical information that will enable the United Kingdom milk and milk products industry to reduce the risk associated with contamination of raw milk with MAP. A particular strength of this study will be the implementation of experimental designs that will allow for interaction of processing treatments.

Funding Source
Dept. for Environment, Food and Rural Affairs
Project number
Risk Assessment, Management, and Communication