Weller Daniel L, Kovac Jasna, Roof Sherry, Kent David J, Tokman Jeffrey I, Kowalcyk Barbara, Oryang David, Ivanek Renata, Aceituno Anna, Sroka Christopher, Wiedmann Martin
1 Department of Food Science, Cornell University, Ithaca, New York 14853.
2 RTI International, Research Triangle Park, North Carolina 27709.
J Food Prot. 2017 Jul;80(7):1214-1221. doi: 10.4315/0362-028X.JFP-16-419.
Although wildlife intrusion and untreated manure have been associated with microbial contamination of produce, relatively few studies have examined the survival of Escherichia coli on produce under field conditions following contamination (e.g., via splash from wildlife feces). This experimental study was performed to estimate the die-off rate of E. coli on preharvest lettuce following contamination with a fecal slurry. During August 2015, field-grown lettuce was inoculated via pipette with a fecal slurry that was spiked with a three-strain cocktail of rifampin-resistant nonpathogenic E. coli. Ten lettuce heads were harvested at each of 13 time points following inoculation (0, 2.5, 5, and 24 h after inoculation and every 24 h thereafter until day 10). The most probable number (MPN) of E. coli on each lettuce head was determined, and die-off rates were estimated. The relationship between sample time and the log MPN of E. coli per head was modeled using a segmented linear model. This model had a breakpoint at 106 h (95% confidence interval = 69, 142 h) after inoculation, with a daily decrease of 0.70 and 0.19 log MPN for 0 to 106 h and 106 to 240 h following inoculation, respectively. These findings are consistent with die-off rates obtained in similar studies that assessed E. coli survival on produce following irrigation. Overall, these findings provide die-off rates for E. coli on lettuce that can be used in future quantitative risk assessments.
尽管野生动物入侵和未经处理的粪便与农产品的微生物污染有关，但相对较少的研究考察了污染（如通过野生动物粪便飞溅）后大肠杆菌在田间条件下在农产品上的存活情况。本实验研究旨在估计用粪便悬液污染收获前生菜后大肠杆菌的死亡速率。2015年8月，通过移液器向田间种植的生菜接种含有耐利福平非致病性大肠杆菌三菌株混合物的粪便悬液。接种后在13个时间点（接种后0、2.5、5和24小时，此后每24小时直至第10天）分别收获10个生菜头。测定每个生菜头上大肠杆菌的最可能数（MPN），并估计死亡速率。使用分段线性模型对采样时间与每个生菜头大肠杆菌对数MPN之间的关系进行建模。该模型在接种后106小时（95%置信区间=69，142小时）有一个断点，接种后0至106小时和106至240小时大肠杆菌对数MPN每日分别下降0.70和0.19。这些发现与评估灌溉后大肠杆菌在农产品上存活情况的类似研究中获得的死亡速率一致。总体而言，这些发现提供了生菜上大肠杆菌的死亡速率，可用于未来的定量风险评估。
