Fate of Escherichia coli0157 : H7 on fresh-cut apple tissue and its potential for transmission by fruit flies

Pathogenic Escherichia coli O157:H7, as well as nonpathogenic strains ATCC 11775 and ATCC 23716, grew exponentially in wounds on Golden Delicious appl e fruit. The exponential growth occurred over a longer time period on fruit inoculated with a lower concentration of the bacterium than on fruit inocu lated with a higher concentration. The bacterium reached the maximum popula tion supported in the wounds regardless of the initial inoculum concentrati ons. Populations of E. coli O157:H7 in various concentrations of sterilized apple juice and unsterilized cider declined over time and declined more qu ickly in diluted juice and cider. The decline was greater in the unsteriliz ed 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. E xperiments on the transmission of E. coli by fruit flies, collected from a compost pile of decaying apples and peaches, were conducted with strain F-1 1775, a fluorescent transformant of nonpathogenic E, coli ATCC 11775. Fruit dies were easily contaminated externally and internally with E, coli F-117 75 after contact with the bacterium source. The flies transmitted this bact erium to uncontaminated apple wounds, resulting in a high incidence of cont aminated wounds. Populations of the bacterium in apple wounds increased sig nificantly during the first 48 h after transmission. Further studies under commercial conditions are necessary to confirm these findings.