Behavior of Hemorrhagic Escherichia coli O157:H7 During the Manufacture of Cottage Cheese

Abstract

The ability of enterohemorrhagic Escherichia coli O157:H7 to grow and survive during the manufacture of Cottage cheese was determined. Pasteurized skim milk artificially contaminated with E. coli O157:H7 was used to make Cottage cheese by the washed curd method. E. coli O157:H7 was enumerated by surface plating samples on MacConkey sorbitol agar with 5-bromo-4-chloro-3-indoxyl-β-D-glucuronic acid cyclohexylammonium salt (MSA-BCIG) and incubating at 42°C for 24 h. The heat treated samples were previously inoculated into a modified EC broth with novobiocin and incubated static at 35°C for 24 h. Sorbitol and β-glucuronidase negative colonies were picked from MSA-BCIG, spread on Levine eosin methylene blue agar plates and phenol red sorbitol agar plates with 4-methylumbelliferyl-β-D-glucuronide (PRS-MUG) added for confirmation. E. coli O157:H7 increased 100-fold in numbers during the manufacturing process, but death occurred during cooking of the curd and whey. The pH and acidity did not halt the growth of this pathogen during the manufacture of the cheese; furthermore, the values of these parameters were the same between the contaminated and control samples.