Effect of turbulent-flow pasteurization on survival of Mycobacterium aviumsubsp paratuberculosis added to raw milk

A pilot-scale pasteurizer operating under validated turbulent flow (Reynold s number, 11,050) was used to study the heat sensitivity of Mycobacterium a vium subsp. paratuberculosis added to raw milk. The ATCC 19698 type strain, ATCC 43015 (Linda, human isolate), and three bovine isolates were heated i n raw whole milk for 15 s at 63, 66, 69, and 72 degreesC in duplicate trial s. No strains survived at 72 degreesC for 15 s; and only one strain survive d at 69 degreesC. Means of pooled D values (decimal reduction times) at 63 and 66 degreesC were 15.0 2.8 s (95% confidence interval) and 5.9 +/- 0.7 s (95% confidence interval), respectively. The mean extrapolated D-72 degree sC was <2.03 s. This was equivalent to a >7 log(10) kill at 72 degreesC for 15 s (95% confidence interval). The mean Z value (degrees required for the decimal reduction time to traverse one log cycle) was 8.6 degreesC. These five strains showed similar survival whether recovery was on Herrold's egg yolk medium containing mycobactin or by a radiometric culture method (BACTE C). Milk was inoculated with fresh fecal material from a high-level fecal s hedder with clinical Johne's disease. After heating at 72 degreesC for 15 s , the minimum M. avium subsp. paratuberculosis kill was >4 log(10). Properl y maintained and operated equipment should ensure the absence of viable M. avium subsp. paratuberculosis in retail milk and other pasteurized dairy pr oducts. An additional safeguard is the widespread commercial practice of pa steurizing 1.5 to 2 degrees above 72 degreesC.