Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/26/1998
Publication Date: N/A
Technical Abstract: Mycobacterium paratuberculosis (paratb), an acid-fast bacillus that causes enteritis (Johne's disease) in ruminants, has been suggested as an etiological agent of Crohn's disease in humans. The mode of transmission is unclear, however, some evidence suggests that humans may become infected via contaminated milk. We previously demonstrated, using a lab-scale pasteurizer unit designed to simulate the high-temp., short-time method (72C, 15 sec) currently used by commercial dairies, that treatment of raw milk inoculated with M. paratb resulted in killing of all the bacteria. However, M. paratb is an intracellular pathogen that resides within the macrophages of the host and evades destruction. It is unknown whether the macrophage would provide a protective environment during pasteurization of milk, which would enable the bacteria to survive. We evaluated this hypothesis by conducting studies in which we experimentally infected bovine emammary gland macrophages or a bovine macrophage cell line with M. paratb (100:1 bacteria to cell). Twenty-four hours after infection, macrophages were removed from flasks, washed, counted, and added to raw milk to achieve an infection level of 106 CFU of M. paratb per ml of milk. Milk was then treated with the pasteurizer unit at 65C and 72C for 15 seconds. Aliquots of treated milk were placed on ice, sonicated, diluted, and plated onto agar medium. Viable bacteria were counted after 12 weeks of incubation. Results from these experiments demonstrate that heat treatment at either temperature (65C, 72C) effectively killed all M. paratb. This would suggest that the macrophage does not protect the pathogen from penetration of heat during the pasteurization process.