Effect of Storage Temperature on the Behaviour of Escherichia coli O157:H7 and Salmonella enterica Serotype Typhimurium on Salad Vegetables

The behaviour of Escherichia coli O157:H7 and Salmonella Typhimurium on fresh lettuce (Lactuca sativa), cucumber (Cucumis sativus) epidermis and parsley (Petroselinum sativum) under different storage temperatures was studied. Inoculated vegetable pieces were stored at 10 °C, 20 °C and 30 °C and E. coli O157:H7 and S. Typhimurium were enumerated by plate count. At 10 °C, both E. coli O157:H7 and S. Typhimurium declined slowly on all three vegetables whereas at higher temperatures the behaviour was markedly different. On parsley and lettuce at 20 °C S. Typhimurium population returned to roughly the starting count at the end of the experiment whereas it increased in cucumber. Growth of up to 0.9 log cfu/g was observed on parsley for E. coli O157:H7, but population changes on the other vegetables were negligible at 20 °C. At 30 °C growth was observed on all three vegetables for both E. coli O157:H7 and S. Typhimurium. Growth of E. coli O157:H7 and S. Typhimurium increase the risk to the consumer of some types of fresh vegetable. Storage temperature abuse of the above fresh vegetables can lead to food poisoning if not decontaminated appropriately or via cross contamination. This study shows that food safety of fresh produce is improved via storage in chilled temperatures. Even relatively short exposure (a few hours) at higher temperatures can allow growth to occur in all three vegetables thereby increasing the risk to food safety. Chilling fresh vegetables as soon as possible after harvest could prevent growth of pathogens if vegetables are cross-contaminated.