Esseili Malak A, Chin Ashlina, Saif Linda, Miller Sally A, Qu Feng, Lewis Ivey Melanie L, Wang Qiuhong
Food Animal Health Research Program, Department of Veterinary Preventive Medicine, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio 44691, USA.
The Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio 44691, USA.
J Food Prot. 2015 Aug;78(8):1472-80. doi: 10.4315/0362-028X.JFP-14-518.
Leafy greens are increasingly being recognized as an important vehicle for human noroviruses (HuNoV), which cause recurring gastroenteritis outbreaks. Leafy greens often become infected by phytopathogens in the field, which may cause symptoms on the edible parts. Whether plant pathogen infections enhance the survival of HuNoV on leafy greens is unknown. Lettuce and spinach plants were infected with a bacterium, Xanthomonas campestris pv. vitians strain 701a, and with Cucumber mosaic virus strain Fny, respectively. The survival rate of porcine sapovirus (SaV), a HuNoV surrogate, on infected and noninfected postharvest leaves was then assessed. In addition, acibenzolar-S-methyl, a commercial chemical elicitor of plant systemic defense, was used to assess whether stimulating the plant host defense affects the postharvest survival of SaV. Leaves harvested from control and treated plants were inoculated with SaV and incubated for 7 days at 4°C. The infectivity (tissue culture infectious dose affecting 50% of the culture [TCID50]/ml) and RNA (genomic equivalent/ml) titers of SaV were assayed using immunohistochemistry staining and SaV-specific TaqMan real-time reverse transcription PCR. Our results showed that cucumber mosaic virus Fny induced mild, nonnecrotic symptoms on spinach leaves and had no effect on SaV survival. In contrast, X. campestris pv. vitians 701a induced small localized necrotic lesions and significantly enhanced SaV survival on lettuce leaves. Treatment with acibenzolar-S-methyl was effective in reducing X. campestris pv. vitians 701a-induced lesions on infected lettuce plants but had no direct effect on SaV survival when used on healthy lettuce plants. These findings indicate that phytopathogen-induced necrotic lesions may enhance the postharvest survival of HuNoV on lettuce leaves. Therefore, preventive measures aiming to maintain healthy plants and minimize preharvest biological damage are expected to improve the safety of leafy greens.
绿叶蔬菜越来越被认为是人类诺如病毒（HuNoV）的重要载体，HuNoV可引发反复的肠胃炎疫情。绿叶蔬菜在田间常被植物病原体感染，这可能会在可食用部分产生症状。植物病原体感染是否会提高HuNoV在绿叶蔬菜上的存活率尚不清楚。生菜和菠菜植株分别被野油菜黄单胞菌致病变种701a和黄瓜花叶病毒Fny株系感染。然后评估了猪札幌病毒（SaV，一种HuNoV替代病毒）在感染和未感染的采后叶片上的存活率。此外，使用苯并噻二唑 - S - 甲基（一种植物系统防御的商业化学激发子）来评估刺激植物宿主防御是否会影响SaV的采后存活率。从对照和处理过的植株上收获的叶片接种SaV，并在4°C下孵育7天。使用免疫组织化学染色和SaV特异性TaqMan实时逆转录PCR检测SaV的感染性（影响50%培养物的组织培养感染剂量[TCID50]/ml）和RNA（基因组当量/ml）滴度。我们的结果表明，黄瓜花叶病毒Fny在菠菜叶片上引发了轻微的、非坏死性症状，对SaV存活没有影响。相比之下，野油菜黄单胞菌致病变种701a在生菜叶片上引发了小的局部坏死病变，并显著提高了SaV的存活率。用苯并噻二唑 - S - 甲基处理可有效减少野油菜黄单胞菌致病变种701a在受感染生菜植株上引起的病变，但在健康生菜植株上使用时对SaV存活没有直接影响。这些发现表明，植物病原体诱导的坏死病变可能会提高HuNoV在生菜叶片上的采后存活率。因此，旨在保持植株健康并尽量减少收获前生物损伤的预防措施有望提高绿叶蔬菜的安全性。
