EFFECT OF HIGH-TEMPERATURE, SHORT-TIME (HTST) PASTEURIZATION ON MILK CONTAINING LOW NUMBERS OF MYCOBACTERIUM-PARATUBERCULOSIS

The efficacy of high-temperature, short-time (HTST) pasteurization (72 degrees C/15 s) when low numbers (less than or equal to 10(3) cfu ml( -1)) of Mycobacterium paratuberculosis are present in milk was investi gated. Ran cows' milk spiked with Myco. paratuberculosis (10(3) cfu ml (-1), 10(2) cfu ml(-1), 10 cfu ml(-1), and 10 cfu 50 ml(-1)) was subje cted to HTST pasteurization using laboratory pasteurizing units. Ten b ovine strains of Myco. paratuberculosis were tested in triplicate. Cul ture in BACTEC Middlebrook 12B radiometric medium detected acid-fast s urvivors in 14.8% and 10% of HTST-pasteurized milk samples at the 10(3 ) and 10(2) cfu ml(-1) inoculum levels, respectively, whereas conventi onal culture an Herrold's egg yolk medium containing mycobactin J dete cted acid-fast survivors in only 3.7% and 6.7% of the same milk sample s. IS900-based PCR confirmed that these acid-fast survivors were Myco. paratuberculosis, Net viable Myco. paratuberculosis were isolated fro m HTST-pasteurized milk initially containing either 10 cfu ml(-1) or 1 0 cfu 50 ml(-1).