Effect of heat treatment on the survival of <i>Escherichia Coli</i> O157:H7 in raw milk

Abstract

The survival of Escherichia coli O157:H7 in raw milk treated in experimental pasteurizer was investigated in the year 2010. Raw milk was inoculated with different initial concentrations of E. coli O157:H7 and heated for 15 seconds at temperatures ranging from 69OC to 73OC. E. coli O157:H7 cells were not isolated from the milk samples immediately after thermal treatment. They were however, isolated from 72% of heated samples after variable periods of storage at refrigeration temperature (4OC). The result suggests that a low number of E. coli O157:H7 survived some thermal treatment, but a cold storage in the refrigerator would have been responsible for repairing the thermally injured cells and thus detect this pathogen in milk. The results also revealed that the lower the initial counts of E. coli O157:H7 in raw milk samples the lower their percentage recovery from the heat treated milk. As the infectious dose of E. coli O157:H7 for human is very low, the presence of the organism in milk even in low numbers, is a potential risk for the consumers because this would lead to clinical infection associated with it.