Potential Transference of Escherichia coli O157:H7 from Contaminated Coring Knife to Field-cored Lettuce and Impact of Holding Time and Temperature on Its Growth

Authors: McEvoy, James; Luo, Yaguang - Sunny; Conway, William; ZHOU, BIN - UIUC; FENG, HAO - UIUC

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 8/19/2008
Publication Date: 11/28/2008
Citation: Mcevoy, J.L., Luo, Y., Conway, W.S., Zhou, B., Feng, H. 2008. Potential Transference of Escherichia coli O157:H7 from Contaminated Coring Knife to Field-cored Lettuce and Impact of Holding Time and Temperature on Its Growth. [abstract] International Association for Food Protection.

Interpretive Summary:

Technical Abstract: Field coring is a recent development in iceberg lettuce harvesting, where the outer leaves and the cores of the lettuce heads are removed at the time of harvesting in order to reduce shipping waste and maximize production yield during processing for fresh-cut products. However, research on the effect of field coring and the associated handling on food safety is lacking. The main objective of this study was to evaluate the potential for pathogen transfer via a contaminated coring knife and the effect of holding temperature and duration on pathogen growth. A lettuce coring knife was artificially contaminated with 2 x 10(5) cells of Escherichia coli O157:H7. The knife was used to core successive iceberg lettuce heads. E.coli after populations were determined 0, 4 and 8 hr at 5 and 30 °C. Although there was a gradual decline in the number of E.coli on successively cored lettuce heads, over 50 cfu/g of E.coli was found on up to 9th cored head. With an enrichment procedure, E.coli was found on lettuce heads out to the 20th successive coring. The subsequent growth of E.coli on lettuce heads was significantly affected by the holding time and temperature. At 5 °C no significant growth or loss of viability of E. coli were noted during an 8 h holding period. At 30 °C however, significant increases in E.coli numbers occurred between 0 h to 4 h and 4 h to 8 h. E. coli numbers, regardless of whether the bacteria were cold stressed prior to use as inoculum, increased by approx. 2 logs10 cfu/g at 30 °C from 0 h to 8 h. Total aerobic messophillic bacteria, and yeast and molds also grew on cored lettuce and their growth was affected by time and temperature with significantly higher growth in the 30 °C samples compared to the 5 °C samples at both the 4 h and 8 h sampling times. These findings suggest that E.coli O157:H7 can be transferred via contaminated coring knives; and there was significant growth of E.coli on cored lettuce held at 30 °C for 4 and 8 hr. Following Good Agricultural Practices (GAP) during produce growing and harvesting to prevent pathogen contamination and prompt cooling of the field-cored lettuce to 5 °C or below are critical steps for ensuring produce safety.