Acid tolerance of Escherichia coli O157 : H7 and its survival in apple juice

Outbreaks of diarrhoea and haemolytic uraemic syndrome have been associated with the consumption of apple cider and apple juice. The organism implicat ed in these outbreaks has been Escherichia coli O157:H7, indicating the res istance of the serotype to acidic pH. On comparing the growth of this serot ype with a control strain of E. coli, it was found that strain O157:H7 grew well in trypticase soy broth at pH levels ranging from 2.0 to 9.0, while c ontrol strains failed to grow at pH levels below 4.0 and above 9.0. The gro wth of both strains were inhibited by adding 0.05% of either benzoic acid o r sorbic acid. Similarly, O157:H7 grew well in both natural (unpasteurized) as well as in pasteurized apple juice and the growth was inhibited by addi ng 0.1% of either benzoic acid or sorbic acid. Control strains of E. coli f ailed to grow in either types of apple juice. The possible sources of conta mination of natural apple juice with O157:H7 serotype are discussed.