Heat Inactivation of Mycobacterium avium subsp paratuberculosis in Aseptically Prepared Ground Beef

Mycobacterium avium subsp. paratuberculosis (Map) is the etiologic agent of Johne's disease in bovine and other ruminants. Concern for public health was raised when the organism was also suggested to be responsible for Crohn's disease in humans, although the evidence remains inconclusive. Nonetheless, limiting human exposure to Map is viewed as a proper precautionary measure. Hence, the efficacy of heat treatment to control the organism in milk has been studied but it has not been studied to the same extend in meat. In this study, aseptically prepared ground beef was obtained from beef semimembranosus muscle and inoculated with two stains of Map (ATCC 7080 and gN27) to determine the decimal reduction time (D-value) and temperature sensitivity (z-value) for each strain. A 25 g sample of meat was inoculated with 100 ul of culture to a final concentration of 10(7) cfu/g. The inoculum was evenly distributed in the meat, which was spread in a thin (2 mm) layer of to maximise heat transfer. Treatments were performed at 55, 60, 65 and 70 degrees C for times allowing a minimum 5-log reduction. D-values decreased significantly with temperature (P < 0.05) ranging from 80.5 +/- 6.1 minutes to 12 +/- 1 seconds for both Map strains. When compared to Escherichia coli ATCC 25922 and Enterococcus faecalis ATCC 7080, D-values were significantly lower for E. coli (P < 0.05) whereas E. faecalis was not consistently more resistant than the two Map strains and, therefore, cannot be used as a surrogate strain for Map control with heat treatment. The z-values were not significantly different (P > 0.05) amongst the four strains and ranged from 5.6 +/- 0.1 degrees C to 6.2 +/- 0.3 degrees C. The results suggest that a low concentration of Map could be controlled with conventional cooking methods.