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

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.
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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.
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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.