Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 19, 1998
Publication Date: N/A
Interpretive Summary: During the past decade the bacterium Escherichia coli O157:H7 caused outbreaks of foodborne illness in meats and unpasteurized apple cider. E. coli O157:H7 can survive but not grow in apple cider and populations of E. coli O157:H7 can decline in sterilized apple juice and unsterilized cider. However, we found that E. coli O157:H7 can grow rapidly on wounded apple tissue. Fruit flies collected from decaying apples and peaches were artificially contaminated with E. coli (non- pathogenic strain used in experiment for safety reason) and were able to carry the bacterium to apple wounds, where the bacterium population increased during the next 48 hours. Ability of E. coli )157:H7 to grow on apple tissue indicates a new pathway of foodborne contamination.
Pathogenic Escherichia coli O157:H7, as well as nonpathogenic strains ATCC 11775 and ATCC 23716, grew exponentially in wounds on 'Golden Delicious' apple. The exponential growth occurred over a longer time period on fruit inoculated with a lower concentration of the bacterium. Populations of the bacterium reach the carrying capacity of the wounds regardless of the initial inoculum concentrations. Populations of E. coli O157:H7 in various concentrations of sterilized apple juice and unsterilized cider declined over time and declined more quickly in diluted juice and cider. The decline was greater in the unsterilized cider than in juice, which may have resulted from the interaction of E. coli O157:H7 with natural populations of yeasts that increased with time. Experiments on the transmission of E. coli by fruit flies, collected from a compost pile of decaying apples and peaches, were conducted with the fluorescent transformant of nonpathogenic E. coli ATCC F-11775. Fruit flies were easily contaminated externally and internally with E. coli ATCC F-11775 after contact with the bacterium source. The flies transmitted this bacterium to uncontaminated apple wounds resulting in a high incidence of contaminated wounds. Populations of AtCC F-11775 transmitted by fruit flies to apple wounds increased significantly during the first 48 hours after transmission. Further studies under commercial conditions are necessary to confirm these findings.