Greve Josephine D, Zietlow Mark S, Miller Kevin M, Ellingson Jay L E
Department of Food Administration, Kwik Trip, Inc., La Crosse, Wisconsin 54602-2107, USA.
Marshfield Food Safety, LLC, 2302 Kwik Trip Way, La Crosse, Wisconsin 54602-2107, USA.
J Food Prot. 2015 Sep;78(9):1729-32. doi: 10.4315/0362-028X.JFP-14-588.
A total of 720 whole, romaine lettuce heads were purchased from retail locations in the Upper Midwest and assessed for coliform and Escherichia coli contamination and for the presence of E. coli O157:H7. During a 16-month period (August 2010 through December 2011), coliform and E. coli counts were enumerated on Petrifilm, and the presence of E. coli O157:H7 and the virulence gene eae was evaluated by real-time PCR (qPCR). Over half (400 of 720) of the lettuce samples were processed with an immunomagnetic separation step before the qPCR assay. All retail lettuce samples were negative for E. coli O157:H7 when tested with the R.A.P.I.D. LT qPCR targeting a region of the O-antigen, and only two (0.28%) were positive for the eae gene when tested with LightCycler qPCR. On Petrifilm, coliform counts of most lettuce samples (96.4%) were between <10(1) and 10(3) CFU/g, and E. coli counts for nearly all lettuce samples (98.2%) were <10(1) CFU/g. No seasonal trend in coliform and E. coli counts was observed throughout the examination period nor was a difference in coliform counts observed between packaged and nonpackaged lettuce heads. These results contribute to the limited recorded data and understanding of microbial contamination of whole romaine lettuce heads purchased from retail locations, specifically revealing the absence of E. coli O157:H7 and low levels of contamination with coliforms and other E. coli strains.
从美国中西部上游地区的零售点购买了总共720颗完整的长叶生菜头，并对其进行了大肠菌群和大肠杆菌污染以及大肠杆菌O157:H7存在情况的评估。在16个月期间（2010年8月至2011年12月），在Petrifilm上对大肠菌群和大肠杆菌进行计数，并通过实时聚合酶链反应（qPCR）评估大肠杆菌O157:H7和毒力基因eae的存在情况。在进行qPCR检测之前，超过一半（720颗中的400颗）的生菜样本经过了免疫磁珠分离步骤。当使用针对O抗原区域的R.A.P.I.D. LT qPCR检测时，所有零售生菜样本的大肠杆菌O157:H7检测结果均为阴性，而使用LightCycler qPCR检测时，只有两颗（0.28%）的eae基因检测结果为阳性。在Petrifilm上，大多数生菜样本（96.4%）的大肠菌群计数在<10(1)至10(3) CFU/g之间，几乎所有生菜样本（98.2%）的大肠杆菌计数<10(1) CFU/g。在整个检测期间，未观察到大肠菌群和大肠杆菌计数的季节性趋势，也未观察到包装生菜头和未包装生菜头之间大肠菌群计数的差异。这些结果有助于补充有限的记录数据，并增进对从零售点购买的完整长叶生菜头微生物污染情况的了解，具体揭示了不存在大肠杆菌O157:H7以及大肠菌群和其他大肠杆菌菌株的低污染水平。
