[Study on the effects of HTST pasteurization temperatures on Mycobacterium avium subsp. paratuberculosis in an industrial fluid milk-processing system].

Johne disease is ruminant chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP). The domestic animals infected with this pathogen present severe weight loss due to chronic diarrhea and a reduction in lactation yield. These result in enormous economic loss since the affected animals are subsequently subject to artificial selections and disinfection of the environment are absolutely necessary. Furthermore, MAP has been suspected to have pathological relationship to Crohn's disease, human chronic granulomatous enteritis. The bacterium grows slower on solid culture and its colony becomes visible after two months of culture. In Japan, there has been almost no investigation on pasteurization temperature of commercial milk using MAP. It comes from the fact that the growth rate of MAP is very slow and that MAP is a related species to Mycobacterium tuberculosis, which pasteurization condition has been well defined. The studies on the pasteurization conditions of commercial milk have been mainly targeted to reduce the risk of infection to Coxiella and Mycobacterium tuberculosis. However, there has been a concern about the possibility that MAP is remained in pasteurized milk because MAPs form an aggregate and the bacterium at its center may not receive enough heat to get pasteurized. From these reasons, the present study aims to investigate validity of the current pasteurization conditions of commercial milk by implementing experimental pasteurization at various pasteurization temperatures using milk experimentally infected with MAP, and to clarify if MAP is eliminated at these temperatures in order to achieve smooth enforcement of the current ministry order. We conducted plant pasteurization experiment at four pasteurization conditions (high temperature, short time (HTST); 82, 77, 72 degrees C for 15 seconds and low temperature, long time (LTLT); 63 degrees C for 30 minutes) using two MAP strains, ATCC19698 and OKY-20. In conclusion, there appeared no colony of the two MAP strains formed from the milk pasteurized at the four pasteurization conditions examined.