Survival of Escherichia coli O157:H7 and Salmonella on Bruised and Unbruised Tomatoes from Three Ripeness Stages at Two Temperatures

Tomatoes are one of the major fresh produce commodities consumed in the United States. Harvesting tomato fruit at a later stage of development can enhance consumer acceptance but can also increase damage due to bruising. Bruising can affect the quality of whole tomatoes by causing an unacceptable appearance and accelerating decay. Bruising may also facilitate bacterial attachment to the fruit surface and support growth of pathogens. This study evaluated the survival and/or proliferation of Escherichia coli O157:H7 and Salmonella on the surface of artificially bruised and unbruised tomatoes at three ripeness stages (breaker, pink, and red) and two storage temperatures (10 and 20 degrees C). A total of 1,440 tomatoes, 720 for each organism, were analyzed. Both E. coli O157:H7 and Salmonella counts declined significantly (P < 0.05) on the bruised and unbruised tomatoes over the 7-day storage period, by approximately 2.5 and 2.0 log, respectively. E. coli O157:H7 was not detected on pink tomatoes on day 7, whereas Salmonella persisted on the tomato surfaces throughout the 7-day study at all ripeness stages. Bruising had no significant effect (P. 0.05) on the survival of E. coli O157:H7 (CFU per tomato) compared with the unbruised tomatoes, in most cases. Tomatoes from the red ripeness stage showed a significant effect (P < 0.05) of bruising on Salmonella survival at both 10 and 20 degrees C. Similar to the colony count results, the frequency (presence or absence) of inoculated tomatoes with detectable levels of inoculated bacteria decreased significantly (P < 0.05) over time. At the lower temperature, E. coli O157:H7 was recovered from significantly higher (P < 0.05) numbers of breaker and pink tomatoes, whereas there was no effect of temperature on the overall survival of E. coli O157:H7 on red tomatoes. Results from this study are essential for understanding the effects of bruising on produce safety and for producers and packers to develop mitigation strategies to control pathogenic and spoilage organisms.