Liu Da, Cui Yue, Walcott Ronald, Chen Jinru
Department of Food Science and Technology, The University of Georgia, Griffin, Georgia, USA.
Department of Plant Pathology, The University of Georgia, Athens, Georgia, USA.
Appl Environ Microbiol. 2017 Dec 15;84(1). doi: 10.1128/AEM.01888-17. Print 2018 Jan 1.
Vegetable seeds contaminated with bacterial pathogens have been linked to fresh-produce-associated outbreaks of gastrointestinal infections. This study was undertaken to observe the physiological behavior of and enterohemorrhagic (EHEC) cells artificially internalized into vegetable seeds during the germination process. Surface-decontaminated seeds of alfalfa, fenugreek, lettuce, and tomato were vacuum-infiltrated with four individual strains of or EHEC. Contaminated seeds were germinated at 25°C for 9 days, and different sprout/seedling tissues were microbiologically analyzed every other day. The internalization of and EHEC cells into vegetable seeds was confirmed by the absence of pathogens in seed-rinsing water and the presence of pathogens in seed homogenates after postinternalization seed surface decontamination. Results show that 317 (62%) and 343 (67%) of the 512 collected sprout/seedling tissue samples were positive for and EHEC, respectively. The average populations were significantly larger ( < 0.05) than the EHEC populations. Significantly larger populations were recovered from the cotyledon and seed coat tissues, followed by the root tissues, but the mean EHEC populations from all sampled tissue sections were statistically similar, except in pregerminated seeds. Three and two EHEC strains had significantly larger cell populations on sprout/seedling tissues than other strains used in the study. and EHEC populations from fenugreek and alfalfa tissues were significantly larger than those from tomato and lettuce tissues. The study showed the fate of internalized human pathogens on germinating vegetable seeds and sprout/seedling tissues and emphasized the importance of using pathogen-free seeds for sprout production. The internalization of microorganisms into vegetable seeds could occur naturally and represents a possible pathway of vegetable seed contamination by human pathogens. The present study investigated the ability of two important bacterial pathogens, and enterohemorrhagic (EHEC), when artificially internalized into vegetable seeds, to grow and disseminate along vegetable sprouts/seedlings during germination. The data from the study revealed that the pathogen cells artificially internalized into vegetable seeds caused the contamination of different tissues of sprouts/seedlings and that pathogen growth on germinating seeds is bacterial species and vegetable seed-type dependent. These results further stress the necessity of using pathogen-free vegetable seeds for edible sprout production.
受细菌病原体污染的蔬菜种子与新鲜农产品相关的胃肠道感染暴发有关。本研究旨在观察人工内化到蔬菜种子中的鼠伤寒沙门氏菌和肠出血性大肠杆菌（EHEC）细胞在发芽过程中的生理行为。对苜蓿、胡芦巴、生菜和番茄进行表面去污处理后的种子，用四种单独的鼠伤寒沙门氏菌或EHEC菌株进行真空浸润。受污染的种子在25°C下萌发9天，每隔一天对不同的芽苗/幼苗组织进行微生物学分析。在种子内化后进行种子表面去污处理后，通过种子冲洗水中无病原体以及种子匀浆中有病原体，证实了鼠伤寒沙门氏菌和EHEC细胞内化到蔬菜种子中。结果表明，在收集的512个芽苗/幼苗组织样本中，分别有317个（62%）和343个（67%）对鼠伤寒沙门氏菌和EHEC呈阳性。鼠伤寒沙门氏菌的平均数量显著高于（P<0.05）EHEC的数量。从子叶和种皮组织中回收的鼠伤寒沙门氏菌数量显著更多，其次是根组织，但除了催芽种子外，所有采样组织切片中的EHEC平均数量在统计学上相似。三种鼠伤寒沙门氏菌菌株和两种EHEC菌株在芽苗/幼苗组织上的细胞数量显著多于研究中使用的其他菌株。胡芦巴和苜蓿组织中的鼠伤寒沙门氏菌和EHEC数量显著多于番茄和生菜组织中的数量。该研究显示了内化的人类病原体在发芽蔬菜种子和芽苗/幼苗组织上的归宿，并强调了使用无病原体种子进行芽苗生产的重要性。微生物内化到蔬菜种子中可能自然发生，代表了人类病原体污染蔬菜种子的一条可能途径。本研究调查了两种重要的细菌病原体，即鼠伤寒沙门氏菌和肠出血性大肠杆菌（EHEC）在人工内化到蔬菜种子后，在发芽过程中沿着蔬菜芽苗/幼苗生长和传播的能力。该研究的数据显示，人工内化到蔬菜种子中的病原体细胞导致了芽苗/幼苗不同组织的污染，并且发芽种子上病原体的生长取决于细菌种类和蔬菜种子类型。这些结果进一步强调了使用无病原体蔬菜种子进行可食用芽苗生产的必要性。
