Chase Jennifer A, Atwill Edward R, Partyka Melissa L, Bond Ronald F, Oryang David
Western Center for Food Safety, University of California, Davis, 1477 Drew Avenue, Suite 101, Davis, California 95618.
Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 5100 Paint Branch Parkway, College Park, Maryland 20740, USA.
J Food Prot. 2017 May 1;80(5):792-798. doi: 10.4315/0362-028X.JFP-16-307.
A field trial was conducted in July 2011 to quantify the inactivation rate of Escherichia coli O157:H7 when mixed with fecal slurry and applied to romaine lettuce leaves. Lettuce was grown under commercial conditions in Salinas Valley, CA. One-half milliliter of rabbit fecal slurry, containing 6.3 × 107 CFU of E. coli O157:H7, was inoculated onto the upper (adaxial) surface of a lower leaf on 240 heads of lettuce within 30 min after a 2.5-h irrigation event. Forty-eight romaine lettuce heads were collected per event at 2.5 h (day 0.1), 19.75 h (day 0.8), 43.25 h (day 1.8), 67.25 h (day 2.8), and 91.75 h (day 3.8) postinoculation and were analyzed for the concentration of E. coli O157:H7 (Ct). E. coli O157:H7 was detected on 100% of collected heads in concentrations ranging from 340 to 3.40 × 1010 most probable number (MPN) per head. Enumeration data indicate substantial growth of E. coli O157:H7 postinoculation (2.5 h), leading to elevated concentrations, 1 to 3 log above the starting inoculum concentration (Co). By the end of the 92-h trial, we observed a net 0.8-log mean reduction of E. coli O157:H7 compared with Co; however, after accounting for the substantial bacterial growth, there was an overall 2.3-log reduction by the final sampling event (92 h). On the basis of two different regression models that used either the raw data for Ct or log-transformed values of Ct/Co during the period 2.5 to 91.75 h postinoculation, there was an estimated 76 to 80% reduction per day in bacterial counts; however, more accurate predictions of MPN per head of lettuce were generated by using non-log-transformed values of Ct. This study provides insight into the survival of E. coli O157:H7 transferred via splash from a contaminated fecal source onto produce during irrigation. Moreover, these findings can help generate inactivation times following a potential contamination incident.
2011年7月进行了一项田间试验，以量化大肠杆菌O157:H7与粪便浆液混合并施用于生菜叶时的灭活率。生菜在加利福尼亚州萨利纳斯山谷的商业条件下种植。在一次2.5小时的灌溉事件后的30分钟内，将含有6.3×10⁷CFU大肠杆菌O157:H7的0.5毫升兔粪便浆液接种到240株生菜下部叶片的上（近轴）表面。每次事件在接种后2.5小时（第0.1天）、19.75小时（第0.8天）、43.25小时（第1.8天）、67.25小时（第2.8天）和91.75小时（第3.8天）收集48个生菜头，并分析大肠杆菌O157:H7的浓度（Ct）。在100%的收集的生菜头中检测到大肠杆菌O157:H7，浓度范围为每头340至3.40×10¹⁰最可能数（MPN）。计数数据表明接种后（2.5小时）大肠杆菌O157:H7大量生长，导致浓度升高，比初始接种浓度（Co）高1至3个对数。到92小时试验结束时，与Co相比，我们观察到大肠杆菌O157:H7的平均净减少量为0.8个对数；然而，在考虑到大量细菌生长后，到最终采样事件（92小时）时总体减少了2.3个对数。基于两种不同的回归模型，一种使用接种后2.5至91.75小时期间Ct的原始数据，另一种使用Ct/Co的对数转换值，估计细菌数量每天减少76%至80%；然而，通过使用Ct的非对数转换值可以更准确地预测每颗生菜的MPN。本研究深入了解了在灌溉期间通过飞溅从受污染的粪便源转移到农产品上的大肠杆菌O157:H7的存活情况。此外，这些发现有助于在潜在污染事件后生成灭活时间。
