United States Department of Agriculture, Agricultural Research Service (USDA-ARS), Beltsville Agricultural Research Center (BARC), Environmental Microbial & Food Safety Laboratory, 10300 Baltimore Avenue, Bldg 201, BARC-East, Beltsville, MD 20705, USA.
United States Department of Agriculture, Agricultural Research Service (USDA-ARS), Beltsville Agricultural Research Center (BARC), Environmental Microbial & Food Safety Laboratory, 10300 Baltimore Avenue, Bldg 201, BARC-East, Beltsville, MD 20705, USA.
Int J Food Microbiol. 2014 Mar 3;173:48-53. doi: 10.1016/j.ijfoodmicro.2013.12.004. Epub 2013 Dec 7.
Contamination of fresh produce could represent a public health concern because no terminal kill step is applied during harvest or at the processing facility to kill pathogens. In addition, once contaminated, pathogens may internalize into produce and be protected from disinfectants during the postharvest processing step. The objective of the current study was to determine the potential internalization of Escherichia coli O157:H7 into spinach roots and subsequent transfer to the edible parts. Because curli are involved in biofilm formation, we investigated whether their presence influence the internalization of E. coli O157:H7 into spinach. Further, the effect of the spinach cultivar on E. coli O157:H7 internalization was evaluated. Spinach plants were grown in contaminated soil as well as hydroponically to prevent mechanical wounding of the roots and inadvertent transfer of pathogens from the contamination source to the non-exposed plant surfaces. Results showed that E. coli O157:H7 could internalize into hydroponically grown intact spinach plants through the root system and move to the stem and leaf level. The incidence of internalization was significantly higher in hydroponically grown plants when roots were exposed to 7 log CFU/mL compared to those exposed to 5 log CFU/mL. The effect of cultivar on E. coli O157:H7 internalization was not significant (P>0.05) for the analyzed spinach varieties, internalization incidences showing almost equal distribution between Space and Waitiki, 49.06% and 50.94% respectively. Wounding of the root system in hydroponically grown spinach increased the incidence of E. coli O157:H7 internalization and translocation to the edible portions of the plant. Experimental contamination of the plants grown in soil resulted in a greater number of internalization events then in those grown hydroponically, suggesting that E. coli O157:H7 internalization is dependent on root damage, which is more likely to occur when plants are grown in soil. Curli expression by E. coli O157:H7 had no significant effect on its root uptake by spinach plants.
新鲜农产品的污染可能会引起公共卫生关注，因为在收获或加工设施期间，没有应用终端杀灭步骤来杀死病原体。此外，一旦被污染，病原体可能会内化到农产品中，并在收获后加工步骤中免受消毒剂的影响。本研究的目的是确定大肠杆菌 O157:H7 潜在地内化到菠菜根部并随后转移到可食用部分。因为卷曲菌参与生物膜的形成，我们研究了它们的存在是否会影响大肠杆菌 O157:H7 内化到菠菜中。此外，还评估了菠菜品种对大肠杆菌 O157:H7 内化的影响。菠菜植物在污染土壤中以及水培中生长，以防止根部机械损伤和病原体从污染源无意中转移到未暴露的植物表面。结果表明，大肠杆菌 O157:H7 可以通过根系内化到水培生长的完整菠菜植物中，并移动到茎和叶水平。与暴露于 5 log CFU/mL 的植物相比，暴露于 7 log CFU/mL 的根系的水培植物中内化的发生率明显更高。分析的菠菜品种对大肠杆菌 O157:H7 内化的影响没有统计学意义（P>0.05），内部化发生率在 Space 和 Waitiki 之间几乎相等，分别为 49.06%和 50.94%。水培菠菜根系的损伤增加了大肠杆菌 O157:H7 的内化发生率和向植物可食用部分的转移。在土壤中生长的植物的实验污染导致更多的内化事件发生，而不是在水培中生长的植物，这表明大肠杆菌 O157:H7 的内化依赖于根系损伤，当植物在土壤中生长时，这种损伤更有可能发生。大肠杆菌 O157:H7 卷曲菌的表达对其被菠菜植物根部吸收没有显著影响。
