Behavior of Escherichia coli O157:H7 in tomato and processed tomato products

The survival of E. coli O157:H7 in acid foods for weeks and its prolonged survival in refrigerated acid foods are well documented. This prompted the study to evaluate survival of E. coli O157:H7 in tomato and processed tomato products. The pH of the various products ranged from 4.2 to 4.8 and some products contained preservatives such as vinegar. Samples were separately inoculated with a mixture of four E. coli O157:H7 strains previously isolated from hamburger meat at lower and higher initial inoculum levels, incubated at 4 and 25 degrees C and assayed for survival at regular intervals. In fresh whole tomato, growth was detected until day 4 and complete elimination was observed at day 7 at room temperature incubation. At refrigeration temperature, counts decreased slightly but survival was noted until day 10. In processed whole tomato, similar patterns were seen at room temperature incubation, but elimination was not observed until day 16. At refrigeration temperatures counts at day 16 were higher than the initial inoculum level. In processed tomato juice, the test strains kept on growing for over 20 days at room temperature storage, whereas at refrigeration temperature, the initial number was more or less maintained until day 23. In processed tomato sauce, incubated at room temperature, a sharp decline in number until day 6 was followed by a sharp increase in number until day 16. At refrigeration temperature, the test strain survived until day 16 with slight decrease in number. The test strains were eliminated in ketchup within 2 days at room temperature, whereas elimination was not achieved until day 8 at refrigeration temperature. In pasta sauce and snack sauce, although elimination was observed at days 11 and 7, respectively, at room temperature incubation, the test strains survived for about 22 days at refrigeration temperature without much decrease in count. Patterns were similar at higher levels of initial inoculation, but it took longer to achieve elimination of the test strains. This study demonstrated that E. coli O157:H7 can survive markedly in various tomato products, and the survival is notably prolonged at refrigeration temperatures.