New research shows successful elimination of the Johne’s organism in milk depends on the type of pasteurization used and the number of organisms present in the milk.

The ability of commercial pasteurization to kill the Johne’s organism in milk destined for human consumption continues to elude researchers. However, new research findings may bring them one step closer to knowing the answer to the question, “Does pasteurization destroy the Johne’s organism in milk?”

Canadian research conducted at the University of Guelph in Ontario suggests commercial batch pasteurization may be more effective than high-temperature, short-time (HTST) pasteurization at destroying Mycobacterium paratuberculosis — the organism that causes Johne’s disease — in milk.

The researchers spiked milk samples with 1,000 colony-forming units (cfu) of M. paratuberculosis per milliliter, 100,000 cfu per milliliter or 10 million cfu per milliliter. They found no live organisms in the milk samples exposed to batch pasteurization — the method by which milk is heated to 145 F and held there for 30 minutes.

However, they detected a small number of live organisms in two of the 11 experiments using HTST pasteurization — the process by which milk is heated to 162 F and held there for 15 seconds. The good news is that the organism survived only when present at high levels in the milk — 100,000 cfu per milliliter or more.

In addition to determining the effect of pasteurization on the Johne’s organism, the researchers also wanted to identify the prevalence of the organism in the retail milk supply.

The researchers recovered the organism’s DNA in 110 — or 15.5 percent — of 710 retail milk samples purchased at retail stores and dairy plants in southwest Ontario. However, they did not detect any live organisms in the milk samples. (Only the live organisms can carry the disease.)

The ability of pasteurization to kill the Johne’s organism in milk for human use is steeped in controversy. Some studies have shown pasteurization kills the Johne’s organism. Others, however, indicate it does not.

These new findings should give researchers more clues as to how best to prevent human exposure to the Johne’s organism. For instance, a longer holding — say, 25 seconds instead of 15 seconds — during HTST pasteurization may be needed to completely destroy the Johne’s organism. Only more research will tell us for sure.

The results were reported in the December 2002 Journal of Dairy Science.