The fate of Escherichia coli O157:H7 in pasteurized milk

The survival of E. coli O157:H7 was examined in artificially contaminated pasteurized milk stored at 7 degrees C and 20 degrees C for 21 days. E. coli O157:H7 survived for more than 21 days in samples of pasteurized milk. The number of E. coli O157:H7 in the milk was directly correlated with the total bacterial counts. In the first 24h at 7 degrees C the number of E. coli O157:H7 slowly decreased from 43x10(3)/ml to 14x10(3)/ml and then increased from 94x10(3)/ml on the second day to 3 160x10(3)/ml on day 14. After that the number of E. coli O157:H7 slightly decreased to 2 250x10(3)/ml, at the end of the study. In the first three days total bacterial counts slowly increased, while pH also did not change during the same time. After 7 days total bacterial counts increased from 520x10(3)/ml to 31 000x10(3)/ml, while pH declined from 5.98 to 4.96 after 21 days Within the first four days of storage of pasteurized milk at 20 degrees C, the number of E. coli O157:H7 increased from 47x10(3)/ml, to 1 260x10(3)/ml and then rapidly fell to day 7. After that the milk was spoiled and the number of E. coli O157:H7 continued to decrease to 26x10(3)/ml on day 14. Then numbers rapidly rose to 660x10(3)/ml after 21 days. In parallel to the change of E. coli O157:H7 counts in pasteurized milk, total bacterial counts in the first 24h increased, and after that slowly decreased from 920x10(3)/ml to 520x10(3)/ml. The results also showed increased total bacterial counts from 1040x10(3)/ml on the 7 th day to 192 000x10(3)/ml after 21 days. During storage of the milk the pH decreased from 6.70 to 3.94 after 14 days, and then rose to 4.80.