UV Light Inactivation of Mycobacterium avium subsp. paratuberculosis in Milk as Assessed by FASTPlaqueTB Phage Assay and Culture

Leslie C. Altic,1 Michael T. Rowe,2 and Irene R. Grant1*

Institute of Agri-Food and Land Use, School of Biological Sciences, Queen’s University Belfast,1 and Agri-Food and Biosciences Institute for Northern Ireland,2 Belfast, Northern Ireland, United Kingdom

 Received 10 January 2007/Accepted 4 April 2007

    UV light inactivation of Mycobacterium avium subsp. paratuberculosis in Middlebrook 7H9 broth and whole and semiskim milk was investigated using a laboratory-scale UV machine that incorporated static mixers within UV-penetrable pipes. UV treatment proved to be less effective in killing M. avium subsp. paratuberculosis suspended in milk (0.5- to 1.0-log10 reduction per 1,000 mJ/ml) than that suspended in Middlebrook 7H9 broth (2.5- to 3.3-log10 reduction per 1,000 mJ/ml). The FASTPlaqueTB phage assay provided more rapid enumeration of surviving M. avium subsp. paratuberculosis (within 24 h) than culture on Herrold’s egg yolk medium (6 to 8 weeks). Despite the fact that plaque counts were consistently 1 to 2 log10 lower than colony counts throughout the study, UV inactivation rates for M. avium subsp. paratuberculosis derived using the phage assay and culture results were not significantly different (P
0.077).

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