The fate of Escherichia coli 01.57 : H7 in raw milk

The survival of E. coli 0157:H7 was examined in artificially contaminated r aw milk kept at 7 degrees C,18 degrees C and 20 degrees C for 21 days. E. c oli 0157:H7 survived more than 21 days in samples kept at 7 degrees C, 18 d egrees C and 20 degrees C for 21 days E. coli 0157. H7 survived more than 2 7 days in samples kept at;OC and 18 degrees C and for 14 days at 20 degrees C. In the first 3 days in the milk kept at 7 degrees C the number of E. co li 0157:H7 increased from 5.4 log CFU/ml to 7.0 log CFU/ml. and did not cha nge up to day 14, but slightly decreased to 5.9 log CFU/ml at the end of th e study. In parallel to the change of E. coli 0157:H7 counts in raw milk, t otal bacterial counts also changed. In the first 7 days total bacterial cou nts increased from 7.3 log CFU/ml to 8.9 log CFU/ml, then decreased to 7.8 log CFU/m at 14 days and after that the numbers decreased to 6.9 log CFU/ml at the end of the study. During the experiment pH decreased from 6.56 to 5 .58. In the milk kept at 18 degrees C, in the first 3 days, the numbers of E. co li 0157:H7 increased from 5.7 log CFU/ml to 7.3 log CFU/ml and then decreas ed to 5.7 log CFU/ml at 14 days followed by a slow decrease to 4.8 log CFU/ ml on the 21 st day. In the! first 24 h, total bacterial counts increased f rom 7.2 log CFU/ml to 8.4 log CFU/ml, remained at the same value and then s lightly decreased to 7.0 log CFU/ml, at 21 days. During the experiment pH d ecreased from 6.56 to 3.94. During storage of the milk at 20 degrees C an increase of the number of E. coli 0157:H7 from 5.5 log CFU/ml to 7.3 log CFU/ml was determined in the fi rst 3 days. This value remained up to 4 days. After that the number of E. c oli 0157:H7 rapidly decreased to 5.9 log CFU/ml at the 7 th day remaining a t that value up to the 14 th day. Total bacterial counts in the first 24 h increased from 7.3 log CFU/ml to 8.5 CFU/ml, and then decreased to 8.1 log CFU/ml after 14 days. The pH decreased from 6.56 to 3.97 at the end of the investigation.