Heat inactivation of Mycobacterium paratuberculosis in raw milk: are current pasteurization conditions effective?

Abstract

Currently, it is not known whether commercial pasteurization effectively kills Mycobacterium paratuberculosis in contaminated raw milk. Results from holder test tube experiments indicated that a residual population of viable bacteria remained after treatment at 65, 72, 74, or 76°C for 0 to 30 min. Use of a laboratory-scale pasteurizer unit demonstrated that treatment of raw milk at 72°C for 15 s effectively killed all M. paratuberculosis.

Heat inactivation data for Mycobacterium avium subsp. paratuberculosis: implications for interpretation

“…This shows that, with an increasing number of clumped bacteria, tailing will occur. This is in agreement with the observations of Grant et al (1996a), Stabel et al (1997) and Keswani and Frank (1998). Hence, the tailing effect has less to do with a more heat-resistant cell fraction but is most likely to be caused by a fraction of clumps with a high number of cells.…”

“…C clump 10 4 tubes and capillaries but not by¯ow pasteurization in (small-scale) industrial pasteurization units (Grant et al 1996a;Keswani and Frank 1998;Sung and Collins 1998). Several publications describe experiments in which HTST equipment was used (Hope et al 1996;Stabel et al 1997) but, in these publications, only end-point measurements were performed. End-point measurements, however, cannot be used to calculate reliable inactivation kinetics.…”

“…All research groups used different culture conditions to grow MAP and different methods to disrupt cell clumps. Grant did not disrupt MAP clumps at all (Grant et al 1996a;Grant et al 1998) while the other investigators used soni®cation (Stabel et al 1997) or shearing (Keswani and Frank 1998;Sung and Collins 1998) to disrupt the clumps. It is reasonable to believe that these treatments may also have an effect on the sensitivity of cells to a subsequent heat shock.…”

“…In such a process milk is preheated, followed by the actual heat treatment and subsequently rapidly cooled to 20 or 4°C. In contrast, however, in most laboratories MAP heat inactivation experiments were performed as a batch process at low temperatures for long holding times, usually followed by a quick cooling on melting ice (Chiodini and Hermon-Taylor 1993;Grant et al 1996a;Grant et al 1996b;Stabel et al 1997;Keswani and Frank 1998). For example, experiments with B. sporothermodurans have shown that batch heating in tubes for less than 1 min results in less inactivation of the cells than occurred under the same conditions in a UHT (Ultra High Temperature) pilot equipment (Huemer et al 1998).…”

“…During the last decade, several experiments on the heat inactivation of MAP have been published (Chiodini and Hermon-Taylor 1993;Grant et al 1996a;Hope et al 1996;Meylan et al 1996;Stabel et al 1997;Grant et al 1998;Keswani and Frank 1998;Sung and Collins 1998;Grant et al 1999). These experiments differ in the way MAP is grown, the heat is applied, inactivation data are obtained, cell clumps are handled and cfu are quanti®ed (see also Table 1).…”