Heat inactivation of Mycobacterium paratuberculosis in raw milk: are current pasteurization conditions effective?
Mycobacterium paratuberculosis, an acid-fast bacillus which causes enteritis 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. Currently, it is not known whether commercial pasteurization effectively kills M. paratuberculosis in contaminated raw milk. Initially, we designed experiments utilizing the holder-test tube method, simulating methodologies utilized in other laboratories, to determine optimal time/temperature combinations for effective inactivation of large numbers of M. paratuberculosis (108 CFU/ml). Results from these experiments indicate a significant reduction in viable bacterial numbers was achieved at 72°C but mean time for optimal killing exceeded industry recommendations of 15 seconds at that temperature. Indeed, a residual population of viable M. paratuberculosis was detectable after 30 min incubation at 65, 72, 74 or 76°C. In subsequent experiments, a laboratory-scale pasteurizer unit designed to simulate the high-temperature, short-time method (72°C, 15 sec) currently used by commercial dairies was evaluated. Results from these experiments demonstrate that treatment of raw milk inoculated with live M. paratuberculosis (104, 106 CFU/ml) at 72°C for 15 seconds effectively killed all the bacteria. Comparison of these two models for testing heat inactivation of M. paratuberculosis indicate that turbulent flow of milk during the pasteurization process appears to be necessary to achieve complete inactivation of contaminating bacteria.
THIS RESEARCH HAS COME UNDER CRITICISM FROM MANY OTHER SCIENTISTS WHO ARGUE THAT STABEL'S METHOLODY IS NOT REPRESENTATIVE OF REAL-WORLD CONDITIONS. WHAT HER RESEARCH SHOWS IS THAT WITH SPIKED MILK IN A LABORATORY SETTING SHE CAN DEMONSTRATE COMPLETE KILLING OF MAP, BUT IT'S A STRETCH TO EXTRAPOLATE THESE RESULTS TO THE REAL WORLD OF MILK ON THE SUPERMARKET SHELF.
Source: http://www.crohns.org/articles/1997_12_4975-7_aem.htm Contact PARA: http://www.crohns.org/contact.htm
Paratuberculosis Awareness & Research Association