The test Actiphage® was found to detect just 1-2 cells per 50ml, providing milk producers and processors the opportunity to further improve dairy quality assurances as part of production line processes.
MAP in 10% of retail samples
The phage-based assay, developed by PBD Biotech, found viable Mycobacterium avium subspecies paratuberculosis (MAP) in 10.3% of the 386 samples of retail purchased pasteurised milk tested.
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.
In previous milk studies that used culture or PCR-based detection methods, it is unlikely that samples containing less than 100 MAP cells per 50ml would have been detected, explaining why this new more sensitive method found more MAP-positive samples.
Dr Ben Swift, corresponding author of the research and co-founder of PBD Biotech, said, “Dr Cath Rees and I discovered that using the Actiphage test mycobacteria cells could be rapidly detected in multiple sample types, such as blood and milk, at very high sensitivity and specificity.
“Additionally, the phage-based diagnostic can distinguish between viable and non-viable organisms. These research findings emphasise the important role that Actiphage can play within food manufacturing as part of quality assurance programmes, helping to continue building consumer confidence in our already-high standards.”
MAP implicated in human conditions
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.
Dr Berwyn Clarke, CEO of PBD Biotech, commented, “We now have a new research tool at our fingertips that can rapidly detect the presence of MAP in all tissue and fluid at very high sensitivity, providing a real opportunity to improve our understanding of this mycobacteria and its associated diseases.”
Shows for first time MAP shed from udder cells
Although many studies have shown that MAP can be detected in pasteurised milk, this new research reveals that, contrary to previous hypothesis, the mycobacteria was not introduced through poor hygiene standards and faecal contamination but was 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 highly sensitive Actiphage assay, which delivers results in hours, rather than weeks, will enable producers and processors to more efficiently and effectively assess milk as part of the production line.
Given the rapidity of PBD Biotech’s assay and its critical specificity for live cells, there is the potential to perform a larger trial in order to ascertain the ability of this new phage-based method to monitor the efficacy of milk pasteurisation processes on a larger scale.
The phage-based assay has also been successfully used to detect viable MAP in raw milk, powdered infant formula, cheese and in the blood of infected animals.
References for the implication of MAP in the development of Crohn’s disease
Bull et al, 2003. Detection and verification of Mycobacterium avium subsp paratuberculosis in fresh ileocolonic mucosal biopsy specimens from individuals with and without Crohn’s disease. Journal of Clinical Microbiology, 41, 2915-2923
Feller et al, 2007. Mycobacterium avium subspecies paratuberculosis and Crohn’s disease: a systematic review and meta-analysis. Lancet Infectious Diseases. 7, 607-613
Rhodes et al, 2014. Mycobacterium avium Subspecies paratuberculosis: Human Exposure through Environmental and Domestic Aerosols. Pathogens. 3,557-595.