This action was prompted by the findings of laboratory pasteurization studies at Queen's University Belfast (QUB) which appeared to indicate that an extended holding time would be more effective in killing M. paratuberculosis survival problem in 1998 by extending the holding time for heat treatment of liquid milk to 25 s at 72☌ ( 1). Despite the uncertainty surrounding the mechanism of apparent heat tolerance, much of the United Kingdom dairy industry responded to the potential M. Bacteria in the center of large clumps may be protected and may require additional heating to be inactivated, or alternatively, because the clumps contain up to 10,000 cells, a proportion of the cells will survive a nonsterilizing heat treatment. paratuberculosis may be influenced by its tendency to occur as clumps of cells ( 9, 15). Thermal death information suggests that the heat resistance of M. paratuberculosis may survive HTST pasteurization of milk on occasion. paratuberculosis ( 2, 6, 10, 13, 15, 17, 19, 20, 27) and studies of pasteurized naturally infected milk ( 8, 12), showing that low levels of viable M. However, there is a growing body of evidence, from both laboratory pasteurization studies involving milk spiked with laboratory-grown M. paratuberculosis present in milk would also be effectively killed by pasteurization of milk at 72☌ for 15 s (so-called high-temperature, short-time pasteurization). Time-temperature conditions used to pasteurize milk were originally designed to kill Mycobacterium bovis, the cause of tuberculosis in cattle and potentially humans and a relative of M. paratuberculosis centers on its apparent heat resistance. The concern to the milk and milk products industry about M. Consequently, any colony count reported for milk when chemical decontamination has been applied is an underestimate of the real number of M. paratuberculosis from milk necessitates a chemical decontamination treatment which will have an adverse effect on the viability of a proportion of the M. paratuberculosis cells present in naturally infected raw milk cannot be accurately determined, as the culture of M. paratuberculosis may be naturally present in milk produced by an infected cow ( 26, 28) or it may gain access to the milk as the result of fecal contamination during the milking process. paratuberculosis may be transmitted to humans via cows' milk. If there is a link between Johne's disease and Crohn's disease, then M. paratuberculosis is a causative agent of some or all cases of Crohn's disease, but a causal link remains a plausible hypothesis ( 4, 21, 22, 24).

Recent reviews of the available evidence concluded that there was insufficient evidence to prove or disprove that M. paratuberculosis, may also be associated with Crohn's disease, an inflammatory bowel disease in humans, although the potential link remains the matter of much debate. The causative agent of Johne's disease in dairy cattle, Mycobacterium avium subsp. paratuberculosis cells would have been present as predominantly declumped cells, which may possibly explain the greater inactivation achieved by the combination of pasteurization and homogenization. Consequently, when HTST pasteurization was being applied to homogenized milk, the M. paratuberculosis cells were reduced to single-cell or “miniclump” status by homogenization at 2,500 lb/in 2. These experiments demonstrated that large clumps of M. paratuberculosis broth suspensions was subsequently assessed using a Mastersizer X spectrometer. The impact of homogenization on clump size distribution in M. paratuberculosis cells was estimated to be 10 to 20 CFU/150 ml, and the reduction in numbers achieved by HTST pasteurization with or without homogenization was estimated to be 4.0 to 5.2 log 10. Where colony counts were obtained, the number of surviving M. Heat treatments incorporating homogenization at 2,500 lb/in 2, applied upstream (as a separate process) or in hold (at the start of a holding section), resulted in significantly fewer culture-positive samples than pasteurization treatments without homogenization ( P < 0.001 for those in hold and P < 0.05 for those upstream).

paratuberculosis had been completely inactivated by HTST pasteurization, alone or in combination with homogenization. paratuberculosis was cultured from 27 (3.3%) of 816 pasteurized milk samples overall, 5 on Herrold's egg yolk medium and 22 by BACTEC culture. paratuberculosis was investigated using a pilot-scale commercial high-temperature, short-time (HTST) pasteurizer and raw milk spiked with 10 1 to 10 5 M. The effect of various pasteurization time-temperature conditions with and without homogenization on the viability of Mycobacterium avium subsp.

Pasteurization unit calculation formula