THERMAL TOLERANCE OF MYCOBACTERIUM-PARATUBERCULOSIS

D values (decimal reduction time; the time required to kill 1 log conc entration of bacteria) were determined for both human and bovine strai ns (Dominic, Ben, BO45, and ATCC 19698) of Mycobacterium paratuberculo sis in 50 mM lactate solution (pH 6.8) and in milk at four temperature s (62, 65, 68, and 71 degrees C), Viable M. paratuberculosis organisms were quantified by a radiometric culture method (BACTEC), Thermal dea th curves for the M. paratuberculosis strains tested were generally li near, with R-2 of greater than or equal to 0.90, but a few curves (R-2 , 0.80 to 0.90) were better described by a quadratic equation, The hum an strains (Dominic and Ben) had similar D values in milk and in lacta te solution. However, D values for the bovine strains (BO45 and ATCC 1 9698) were significantly different depending on the menstruum, D value s for low-passage clinical strains (Dominic, Ben, and BO45) were lower than those of the high-passage laboratory strain (ATCC 19698), The D value based on pooled data for clinical strains of M. paratuberculosis in milk at 71 degrees C (D-71 degrees C) was 11.67 s. Pooled D-62 deg rees C, D-65 degrees C, and D-68 degrees C of clinical M. paratubercul osis strains in milk were 228.8, 47.8, and 21.8 s, respectively, The Z value (the temperature required for the decimal reduction time to tra verse 1 log cycle) of clinical strains in milk was 7.11 degrees C. The D values of clumped and single M. paratuberculosis cells were not sig nificantly different, The D values of all M. paratuberculosis strains tested were considerably higher than those published for Listeria, Sal monella, and Coxiella spp, and estimated for Mycobacterium bovis, indi cating that M. paratuberculosis is more thermally tolerant, This study supports the premise that M. paratuberculosis may survive high-temper ature, short-time pasteurization when the initial organism concentrati on is greater than 10(1) cells/ml.