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JOHNE'S INFORMATION CENTER - University of Wisconsin Ñ School of Veterinary Medicine



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Friday, September 14, 2018
Survival of MAP in retail pasteurized milk - England.

Research article summary: This study confirms that viable MAP is found in retail pasteurized milk. Specifically, 10% of 368 semi-skimmed, retail-purchased, pasteurized milk samples were positive for viable MAP using a phage-based assay with PCR confirmation. The study’s primary author, Zara E. Gerrard, is based at the University of Nottingham, Leicestershire, England. The article appears in the journal Food Microbiology 74:57-63, September, 2018.

Abstract: A survey of retail purchased semi-skimmed pasteurised milk (n = 368) for Mycobacterium avium subspecies paratuberculosis (MAP) was conducted between May 2014 and June 2015 across the midlands of England using the Phage-PCR assay. Overall, 10.3% of the total samples collected contained viable MAP cells, confirming that pasteurisation is not capable of fully eliminating human exposure to viable MAP through milk. Comparison of the results gained using the Phage-PCR assay with the results of surveys using either culture or direct PCR suggest that the phage-PCR assay is able to detect lower numbers of cells, resulting in an increase in the number of MAP-positive samples detected. Comparison of viable count and levels of MAP detected in bulk milk samples suggest that MAP is not primarily introduced into the milk by faecal contamination but rather are shed directly into the milk within the udder. In addition results detected an asymmetric distribution of MAP exists in the milk matrix prior to somatic cell lysis, indicating that the bacterial cells in naturally contaminated milk are clustered together and may primarily be located within somatic cells. These latter two results lead to the hypothesis that intracellular MAP within the somatic cells may be protected against heat inactivation during pasteurisation, accounting for the presence of low levels of MAP detected in retail milk.

Comment: Phage-based MAP detection methods provide enhanced analytical sensitivity (lower limit of detection) in comparison with culture-based methods. The body of scientific evidence that MAP is in retail pasteurized dairy products continues to grow making this an important food safety issue. The idea advanced in this publication that MAP occurs in milk primarily due to shedding directly from the udder and that these MAP cells are inside host (cow) cells and that fecal contamination of milk is of less importance is novel and bears further investigation.

A partial list of other studies that have found live MAP in retail dairy products by country:
  • United Kingdom, Applied and Environmental Microbiology, May 2002.
  • United States, Applied and Environmental Microbiology, March 2005.
  • Czech Republic, Journal of Food Protection, May 2005.
  • Brazil, Journal of Dairy Science, December 2012.
  • Cyprus, International Journal of Food Microbiology, September 2015.

PubMed abstract