Survival of Escherichia coli O157:H7, O111:H− and O26:H11 in artificially contaminated chocolate and confectionery products

Abstract To date, the survival of Escherichia coli O157:H7 and other verocytotoxin-producing E. coli (VTEC) in chocolate and other confectionery products has not been fully established, unlike Salmonella , which have been responsible for occasional outbreaks of infection linked to contaminated chocolate and related products, although none of these outbreaks have been related to products produced in the United Kingdom. The United Kingdom Biscuit, Cake, Chocolate and Confectionery Alliance commissioned this study to obtain information on the decline and potential survival of E. coli , particularly verocytotoxin-producing strains, in reduced a w confectionery products chocolate, biscuit cream and mallow. These products were artificially contaminated with high (4 log 10 cfu/g) and low (2 log 10 cfu/g) levels of E. coli O157:H7, O111:H− and O26:H11 and their survival, as affected by storage temperature (10, 22 and 38 °C), was monitored over 12 months. Preliminary studies to establish the best inoculation and recovery procedures indicated that differences between counts on selective and non-selective media used were not sufficiently different to influence the outcome of this study. Irrespective of sample type, rapid decline was observed in products stored at 38 °C and increased survival occurred in products stored at 10 °C. In chocolate (average a w 0.40), these bacteria were detected for up to 43 days in samples stored at 38 °C. At 22 °C they survived for up to 90 days and in product stored at 10 °C they could still be detected after 366 days storage. In biscuit cream (average a w 0.75) they survived for 2 days at 38 °C, 42 days at 22 °C and 58 days at 10 °C. Whilst mallow ( a w ca. 0.73) was not stored at 38 °C, these bacteria could still be detected in samples stored for up to 113 and 273 days at 22 and 10 °C, respectively. The observed prolonged survival of these bacteria under conditions of reduced a w and lowered storage temperature in this study is supported by previous studies with Salmonella and E. coli O157:H7 in other foods. In the same way that Salmonella bacteria can survive for long periods, in excess of 12 months, in chocolate, this study provides evidence that E. coli , including pathogenic strains, can also survive for similar periods of time. Assuming the routes of transmission are similar, controls currently used by the confectionery industry to prevent contamination by Salmonella should also be effective against E. coli , including VT-producing strains, providing that all raw materials have been suitably processed, stored and handled before and during manufacture.