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New assay for mycobacteria in milk

Mycobacteria

A new, highly sensitive test has found that 10% of milk samples contain low levels of mycobacteria pathogens according to research due to be published in Food Microbiology.

The phage-based assay, ActiphageTM, developed by PBD Biotech, can distinguish between viable and non-viable organisms. It found viable Mycobacterium avium subspecies paratuberculosis (MAP) in 10.3% of the 386 samples of retail purchased pasteurised milk tested[5].

Two-thirds of the MAP-positive samples (6.8%) contained just 1-2 detectable MAP cells per 50ml, with a further 1.1% containing more than 10 detectable MAP cells per 50ml.

Previous milk studies using culture or PCR-based detection methods were unlikely to detect less than 100 MAP cells per 50ml, explaining why this new more sensitive method found more MAP-positive samples. MAP causes Johne’s disease, a chronic wasting disease of cattle and other ruminants, which not only affects animal health but has a significant economic impact on the dairy industry hence the need for regular milk testing to detect and monitor herd-level infection.

MAP has also been implicated in the development of Crohn’s disease, with the mycobacteria found in the bowel tissue of a proportion of patients with the condition. However, no causal relationship between MAP and the inflammatory bowel condition has been established.

Although many studies have shown that MAP can be detected in pasteurised milk, this new research reveals that the mycobacteria were not introduced through poor hygiene standards and faecal contamination but were shed directly into the milk samples through somatic or ‘body’ cells within the cow’s udder. The location of MAP internalised within somatic cells may explain why low-levels of the mycobacterium are protected against heat inactivation during pasteurisation.

There is no regulatory MAP count limit for milk or other dairy products, however the new ActiphageTM assay, which delivers results in hours, will enable producers and processors to more efficiently and effectively assess milk as part of the production line. The phage-based assay has also been used to detect viable MAP in raw milk, powdered infant formula, cheese and in the blood of infected animals.

References

5. http://www.pbdbio.com/news/new-research-explains-map-found-in-pasteurise...



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