Adequacy of current pasteurization standards to inactivate Mycobacterium paratuberculosis in milk and phosphate buffer

Mycobacterium avium subspecies paratuberculosis (MAP) inactivation kinetics was studied to assess whether current legislative pasteurization prescriptions are sufficient to reduce this bacterium to an acceptable level in raw milk. To assess possible protective effects of milk components during pasteurization, raw milk and phosphate-buffered saline (PBS) were compared. Analyzing data from three replicate experiments in milk separately gave D60°C-values ranging from 114.3 to 244.5 s and z-values ranging from 4.2 to 6.8 °C; in PBS the ranges were 162.4 to 353.3 s and 4.0 to 9.0 °C, respectively. No statistically significant difference was observed between the heat resistance of MAP in milk versus PBS. The currently prescribed minimum HTST pasteurization conditions (71.7 °C, 15 s) were found to be insufficient to kill MAP in milk in 2 out of 6 replicate experiments, while LTLT pasteurization (minimum 62.7 °C, 30 min) was effective, based on extrapolation of the inactivation data obtained.