Abstract The fate of various Escherichia coli O157:H7 strains including 933, A8993-C32, MF6707, 18731A, EK250 and EF304 during the fermentation and storage of diluted cultured milk drink fermented with Lactobacillus casei ssp. casei CCRC 11197 or L. delbrueckii ssp. bulgaricus CCRC 14009 were investigated in this study. E. coli O157:H7, regardless of strains, grew rapidly in skim milk and reached a maximum population of c. 8·0–9·0 log cfu ml −1after c. 24 h of cultivation in mixed cultures with L. casei ssp. casei or L. delbrueckii ssp. bulgaricus. However, the population of E. coli O157:H7, depending on the strain and the lactic acid bacteria present, declined as cultivation proceeded further. With the inoculation of c. 5·0 log cfu ml −1 E. coli O157:H7, viable cells of this pathogen reduced to non-detectable level in the non-sugar-added cultured drink (pH 3·5) prepared with L. delbrueckii ssp. bulgaricus after one day storage at 7°C. Depending on the strains, E. coli O157:H7 survived in the non-sugar-added cultured drink prepared with L. casei ssp. casei for a period of <1–4 days. Adding sugar to cultured drink extended the survival period of E. coli O157:H7. The extent of the sugar-protective effect varied with different strains of E. coli O157:H7 and the amount of sugar added to the drink.