Pasteurization of Mycobacterium paratuberculosis in whole milk
It is preferable to use commercial pasteurizing units to assess bacterial thermosusceptibility and establish the efficacy of pasteurization because the heating and cooling differentials generated in laboratory heat treatment may not simulate commercial conditions. Seventeen batches of raw milk were loaded with 102-105 CFU/mL of Mycobacterium paratuberculosis and pasteurized in a small scale commercial pasteurizing unit at temperatures ranging from 72-90°C for 15-35 seconds. Up to 20 samples were tested from each batch and M. paratuberculosis was not isolated from 96% (275/286) of pasteurized milk samples, representing 104 reductions in mycobacterial concentrations as radiometric culture could detect about one colony forming unit per milliliter. Viable mycobacteria were not recovered when raw whole milk was loaded with less than 104 mycobacteria per milliliter. They were not detected in any of five batches of milk pasteurized at 72-73°C for 25-35 seconds, which are the minimum conditions applied when this machine is used commercially to correct for laminar flow in the holding tube. At shorter times than recommended no viable bacteria were isolated from seven batches, however small numbers of viable bacteria were cultured from four of eight batches heat treated at 72-73°C for 15 seconds and one of four batches treated at 82-92°C for 15 seconds. In the five batches where M. paratuberculosis was recovered the raw whole milk was loaded with more than 104 mycobacteria per milliliter. Survival of M. paratuberculosis in experimentally inoculated batches of milk in the small-scale commercial unit cannot be directly extrapolated to commercial pasteurization of naturally infected milk in dairy factories because of artificially high mycobacterial loads used in these experiments, possible differences in the thermosusceptibility of laboratory cultured mycobacteria, and features of the small-scale unit. Pasteurization in a small-scale commercial unit used in these experiments appears to be more efficient at killing mycobacteria than laboratory heat treatment systems.
BY USING SMALL-SCALE PASTEURIZERS INSTEAD OF LARGER COMMERCIAL PASTEURIZERS, AND BY USING SPIKED MILK INSTEAD OF MILK DIRECT FROM THE FARM, THIS RESEARCH HAS LIMITED RELEVANCE TO THE REAL-WORLD QUESTION -- DOES PASTEURIZATION KILL ALL MAP ORGANISMS OR DOESN'T IT?.
Source: http://www.crohns.org/articles/1996_09_368-73_5icp.htm Contact PARA: http://www.crohns.org/contact.htm
Paratuberculosis Awareness & Research Association