New Tool Explains Live Mycobacteria Found in Retail Milk by Berwyn Clarke in CDVS in Lupine Publishers
Most consumers of dairy products accept that pasteurization provides a
guarantee that products are safe to eat and drink. However, research [1]
using a new highly sensitive technology has revealed that live
mycobacteria can exist in retail milk even after pasteurization and
explains how this may happen. Live Mycobacterium avium subspecies
paratuberculosis (MAP) - which causes Johne’s disease in cattle and has
been implicated in Crohn’s disease in humans - was found in just over
10% of shop-bought pasteurized milk samples that were tested in the UK.
The prevalence of MAP is higher than previous studies have shown due to
the high sensitivity of the new phage-based technology that was used to
conduct the milk testing. In the study of 386 samples of
retail-purchased milk, Actiphage was able to detect live mycobacteria at
levels as low as 1-2 cells per 50ml in comparison to other tests that
cannot detect cell-counts lower than 100 cells. There is a growing body
of research that implicates MAP in the development of Crohn’s disease
[2], with MAP found in the bowel tissue of a proportion of patients with
the condition. Although no causal relationship between MAP and Crohn’s
has been directly established the dairy industry recognizes that
limiting human exposure to MAP would be sensible on a precautionary
principle [3]. Furthermore, there are clinical trials underway with
anti-mycobacterial drugs that are directly assessing the benefit in
Crohn’s disease. Some retailers are already removing dairy farmers from
their milk pool if they are not engaged with Johne’s control plans.
The Actiphage assay, developed by PBD Biotech, uses a virus (phage) that
finds, infects and replicates in viable mycobacteria cells. Within
hours the virus breaks open the mycobacteria cells, releasing DNA
determining whether live organisms were present in the sample. Previous
quality control procedures to monitor the levels of MAP in pasteurized
milk have been difficult as these mycobacteria are extremely slow
growing. Culturing these
bacteria takes up to 18 weeks to determine if any MAP cells have
survived a food safety or control process and the sensitivity of the
procedure is low. The new phage-based detection method, which was used
within the research published in the Elsevier journal of Food
Microbiology (September 2018) [1], allowed experiments to be performed
quickly (6-8 hours); providing the insight dairy producers and
processors need to further improve control measures. The test’s
underlying biotechnology was originally used for the detection of human
TB-under the FastPlaque brand - but was only suitable for use on sputum.
Now the highly specific phage-based diagnostic has been optimized, so
it can detect the presence of mycobacteria in blood or milk in just six
hours. Contrary to previous hypotheses, this research also suggests that
MAP does not enter the milk solely due to faecal contamination, but via
somatic cells within the udder. This intracellular location and the
fact that these cells appear to clump may help explain how the
mycobacteria are protected against heat inactivation during
pasteurization and could lead to new processing methods to ensure the
mycobacteria are inactivated. Earlier published work in 2016 [4] using
the same technology also demonstrated the presence of live MAP in infant
formula milk further increasing the value of this technology as a
screening tool.
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